feat: implement Room Enchantments system for Enchanter attunement

- Add roomEnchantment field to FloorState (coverage meter 0-100)
- Add 8 room enchantment effect definitions (fire/frost/death/lightning/dark/earth/transference)
- Add room-enchanting discipline with perks (room-coverage-rate capped, resonant-stamps once, 8 unlock perks)
- Add room enchantment combat tick phase (after DoT) with coverage growth and effect application
- Add coverage carryover between rooms via resonant-stamps perk
- Add RoomDisplay coverage bar and effect magnitude UI
- Add room-enchantments-utils.ts for coverage/effect computation
- Extract combat-room-enchantments.ts to keep combat-actions.ts under 400 lines
- Add 25 tests covering all acceptance criteria (AC-1 through AC-22)

src/lib/game/__tests__/room-enchantments.test.ts

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+// ─── Room Enchantments System Tests ────────────────────────────────────────────
+// Tests for coverage computation, effect application, and equipment scanning.
+
+import { describe, it, expect } from 'vitest';
+import {
+  computeCoveragePerTick,
+  applyRoomEnchantmentTick,
+  getEquippedRoomEnchantments,
+  isRoomEnchantmentSpecialId,
+  getRoomEnchantmentBaseMagnitude,
+  getRoomEnchantmentName,
+  getRoomEnchantmentColor,
+  BASE_COVERAGE_RATE,
+} from '../utils/room-enchantments-utils';
+import type { EnemyState, EquipmentInstance } from '../types';
+
+// ─── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeEnemy(overrides: Partial<EnemyState> = {}): EnemyState {
+  return {
+    id: 'enemy-1',
+    name: 'Test Enemy',
+    hp: 100,
+    maxHP: 100,
+    armor: 0.1,
+    dodgeChance: 0.05,
+    element: 'fire',
+    activeEffects: [],
+    effectiveArmor: 0.1,
+    ...overrides,
+  };
+}
+
+function makeEquipmentInstance(enchantmentIds: string[]): EquipmentInstance {
+  return {
+    instanceId: 'test-instance',
+    typeId: 'test-boots',
+    name: 'Test Boots',
+    enchantments: enchantmentIds.map(id => ({
+      effectId: id,
+      stacks: 1,
+      capacityCost: 20,
+    })),
+    usedCapacity: 20,
+    totalCapacity: 30,
+    rarity: 'common',
+    quality: 1,
+  };
+}
+
+// ─── computeCoveragePerTick ────────────────────────────────────────────────────
+
+describe('computeCoveragePerTick', () => {
+  it('returns base rate (0.2) with no discipline bonus', () => {
+    expect(computeCoveragePerTick(0)).toBe(BASE_COVERAGE_RATE);
+    expect(computeCoveragePerTick(0)).toBe(0.2);
+  });
+
+  it('adds discipline bonus to base rate', () => {
+    expect(computeCoveragePerTick(0.03)).toBe(0.23);
+    expect(computeCoveragePerTick(0.12)).toBe(0.32);
+  });
+});
+
+// ─── isRoomEnchantmentSpecialId ────────────────────────────────────────────────
+
+describe('isRoomEnchantmentSpecialId', () => {
+  it('returns true for valid room enchantment specialIds', () => {
+    expect(isRoomEnchantmentSpecialId('room_fire_damage')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_frost_debuff')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_death_damage')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_lightning_damage')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_dark_dodge_debuff')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_earth_armor_debuff')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_transference_buff')).toBe(true);
+    expect(isRoomEnchantmentSpecialId('room_transference_regen')).toBe(true);
+  });
+
+  it('returns false for non-room enchantment specialIds', () => {
+    expect(isRoomEnchantmentSpecialId('spellEcho10')).toBe(false);
+    expect(isRoomEnchantmentSpecialId('fireBlade')).toBe(false);
+    expect(isRoomEnchantmentSpecialId('')).toBe(false);
+  });
+});
+
+// ─── getRoomEnchantmentBaseMagnitude ───────────────────────────────────────────
+
+describe('getRoomEnchantmentBaseMagnitude', () => {
+  it('returns correct base magnitudes', () => {
+    expect(getRoomEnchantmentBaseMagnitude('room_fire_damage')).toBe(5);
+    expect(getRoomEnchantmentBaseMagnitude('room_frost_debuff')).toBe(0.10);
+    expect(getRoomEnchantmentBaseMagnitude('room_death_damage')).toBe(3);
+    expect(getRoomEnchantmentBaseMagnitude('room_lightning_damage')).toBe(3);
+    expect(getRoomEnchantmentBaseMagnitude('room_dark_dodge_debuff')).toBe(0.10);
+    expect(getRoomEnchantmentBaseMagnitude('room_earth_armor_debuff')).toBe(0.05);
+    expect(getRoomEnchantmentBaseMagnitude('room_transference_buff')).toBe(0.05);
+    expect(getRoomEnchantmentBaseMagnitude('room_transference_regen')).toBe(0.10);
+  });
+
+  it('returns 0 for unknown specialId', () => {
+    expect(getRoomEnchantmentBaseMagnitude('unknown')).toBe(0);
+  });
+});
+
+// ─── getRoomEnchantmentName ────────────────────────────────────────────────────
+
+describe('getRoomEnchantmentName', () => {
+  it('returns correct display names', () => {
+    expect(getRoomEnchantmentName('room_fire_damage')).toBe('Blazing Footsteps');
+    expect(getRoomEnchantmentName('room_frost_debuff')).toBe('Frozen Trail');
+    expect(getRoomEnchantmentName('room_death_damage')).toBe('Necrotic Tread');
+    expect(getRoomEnchantmentName('room_lightning_damage')).toBe('Shocking Stride');
+    expect(getRoomEnchantmentName('room_dark_dodge_debuff')).toBe('Shadow Patch');
+    expect(getRoomEnchantmentName('room_earth_armor_debuff')).toBe('Scoured Earth');
+    expect(getRoomEnchantmentName('room_transference_buff')).toBe('Transference Grounds');
+    expect(getRoomEnchantmentName('room_transference_regen')).toBe('Conductive Path');
+  });
+});
+
+// ─── getEquippedRoomEnchantments ───────────────────────────────────────────────
+
+describe('getEquippedRoomEnchantments', () => {
+  it('returns empty array when no feet equipped', () => {
+    const result = getEquippedRoomEnchantments({}, {});
+    expect(result).toEqual([]);
+  });
+
+  it('returns empty array when feet has no room enchantments', () => {
+    const instances = { 'inst-1': makeEquipmentInstance(['spell_echo_10']) };
+    const result = getEquippedRoomEnchantments({ feet: 'inst-1' }, instances);
+    expect(result).toEqual([]);
+  });
+
+  it('returns room enchantments from equipped footwear', () => {
+    const instances = { 'inst-1': makeEquipmentInstance(['boots_sigil_fire']) };
+    const result = getEquippedRoomEnchantments({ feet: 'inst-1' }, instances);
+    expect(result).toHaveLength(1);
+    expect(result[0].specialId).toBe('room_fire_damage');
+    expect(result[0].baseMagnitude).toBe(5);
+  });
+
+  it('returns multiple room enchantments from equipped footwear', () => {
+    const instances = { 'inst-1': makeEquipmentInstance(['boots_sigil_fire', 'boots_sigil_frost']) };
+    const result = getEquippedRoomEnchantments({ feet: 'inst-1' }, instances);
+    expect(result).toHaveLength(2);
+    expect(result[0].specialId).toBe('room_fire_damage');
+    expect(result[1].specialId).toBe('room_frost_debuff');
+  });
+});
+
+// ─── applyRoomEnchantmentTick ──────────────────────────────────────────────────
+
+describe('applyRoomEnchantmentTick', () => {
+  it('does nothing when no enemies', () => {
+    const result = applyRoomEnchantmentTick({
+      coverage: 50,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies: [],
+      rawMana: 100,
+    });
+    expect(result.enemies).toEqual([]);
+    expect(result.playerBuffs.castSpeedMultiplier).toBe(0);
+  });
+
+  it('does nothing when no equipped room enchantments', () => {
+    const enemies = [makeEnemy()];
+    const result = applyRoomEnchantmentTick({
+      coverage: 50,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [],
+      enemies,
+      rawMana: 100,
+    });
+    expect(result.enemies[0].hp).toBe(100);
+  });
+
+  it('AC-11: fire DoT scales linearly with coverage', () => {
+    const enemies = [makeEnemy()];
+
+    // At 0% coverage, no damage
+    const r0 = applyRoomEnchantmentTick({
+      coverage: 0,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(r0.enemies[0].hp).toBe(100);
+
+    // At 50% coverage: 5 * 0.5 = 2.5 damage
+    const r50 = applyRoomEnchantmentTick({
+      coverage: 50,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(r50.enemies[0].hp).toBeCloseTo(97.5, 1);
+
+    // At 100% coverage: 5 * 1.0 = 5 damage
+    const r100 = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(r100.enemies[0].hp).toBe(95);
+  });
+
+  it('AC-8: fire DoT hits all living enemies', () => {
+    const enemies = [makeEnemy({ id: 'e1' }), makeEnemy({ id: 'e2' }), makeEnemy({ id: 'e3' })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies,
+      rawMana: 100,
+    });
+    expect(result.enemies[0].hp).toBe(95);
+    expect(result.enemies[1].hp).toBe(95);
+    expect(result.enemies[2].hp).toBe(95);
+  });
+
+  it('AC-8: fire DoT does not damage dead enemies', () => {
+    const enemies = [makeEnemy({ id: 'e1', hp: 0 }), makeEnemy({ id: 'e2' })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies,
+      rawMana: 100,
+    });
+    expect(result.enemies[0].hp).toBe(0);
+    expect(result.enemies[1].hp).toBe(95);
+  });
+
+  it('AC-11: aura magnitude multiplier increases effect', () => {
+    // At 100% coverage with 1.5x multiplier: 5 * 1.0 * 1.5 = 7.5 damage
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1.5,
+      equippedRoomEnchantments: [{ specialId: 'room_fire_damage', baseMagnitude: 5 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(result.enemies[0].hp).toBeCloseTo(92.5, 1);
+  });
+
+  it('AC-10: transference buff returns cast speed multiplier', () => {
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_transference_buff', baseMagnitude: 0.05 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(result.playerBuffs.castSpeedMultiplier).toBe(0.05);
+  });
+
+  it('AC-10: transference regen returns regen per hour', () => {
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_transference_regen', baseMagnitude: 0.10 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(result.playerBuffs.transferenceRegenPerHour).toBe(0.10);
+  });
+
+  it('AC-9: frost debuff reduces enemy dodge chance', () => {
+    const enemies = [makeEnemy({ dodgeChance: 0.3 })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_frost_debuff', baseMagnitude: 0.10 }],
+      enemies,
+      rawMana: 100,
+    });
+    // dodgeChance reduced by 0.10 (10% of 100% coverage)
+    expect(result.enemies[0].dodgeChance).toBeCloseTo(0.20, 2);
+  });
+
+  it('AC-9: earth debuff reduces enemy effective armor', () => {
+    const enemies = [makeEnemy({ effectiveArmor: 0.3 })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_earth_armor_debuff', baseMagnitude: 0.05 }],
+      enemies,
+      rawMana: 100,
+    });
+    expect(result.enemies[0].effectiveArmor).toBeCloseTo(0.25, 2);
+  });
+
+  it('AC-12: multiple enchantments share coverage and apply independently', () => {
+    const enemies = [makeEnemy({ dodgeChance: 0.3 })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [
+        { specialId: 'room_fire_damage', baseMagnitude: 5 },
+        { specialId: 'room_frost_debuff', baseMagnitude: 0.10 },
+      ],
+      enemies,
+      rawMana: 100,
+    });
+    // Fire damage applied
+    expect(result.enemies[0].hp).toBe(95);
+    // Frost debuff applied
+    expect(result.enemies[0].dodgeChance).toBeCloseTo(0.20, 2);
+  });
+
+  it('death DoT deals 3 dmg/tick at 100% coverage', () => {
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_death_damage', baseMagnitude: 3 }],
+      enemies: [makeEnemy()],
+      rawMana: 100,
+    });
+    expect(result.enemies[0].hp).toBe(97);
+  });
+
+  it('dark dodge debuff reduces dodge chance', () => {
+    const enemies = [makeEnemy({ dodgeChance: 0.5 })];
+    const result = applyRoomEnchantmentTick({
+      coverage: 100,
+      auraMagnitudeMultiplier: 1,
+      equippedRoomEnchantments: [{ specialId: 'room_dark_dodge_debuff', baseMagnitude: 0.10 }],
+      enemies,
+      rawMana: 100,
+    });
+    expect(result.enemies[0].dodgeChance).toBeCloseTo(0.40, 2);
+  });
+});
+
+// ─── Coverage cap ──────────────────────────────────────────────────────────────
+
+describe('coverage cap at 100', () => {
+  it('coverage cannot exceed 100 in computeCoveragePerTick usage', () => {
+    // Simulate what the combat tick does: min(100, coverage + rate)
+    const rate = computeCoveragePerTick(0.12); // max tier rate
+    const newCoverage = Math.min(100, 99.9 + rate);
+    expect(newCoverage).toBe(100);
+  });
+});