test: add unit tests for core game logic utilities

Add 5 new test files covering pure utility functions:
- discipline-math.test.ts (42 tests): stat bonus, mana drain, perk tiers,
  discipline activation/progression, unlocked perks, discipline stats
- formatting.test.ts (35 tests): fmt, fmtDec, formatSpellCost,
  getSpellCostColor, formatStudyTime, formatHour
- floor-utils.test.ts (13 tests): getFloorMaxHP, getFloorElement
- combat-utils.test.ts (37 tests): getElementalBonus, getBoonBonuses,
  getIncursionStrength, canAffordSpellCost, deductSpellCost
- mana-utils.test.ts (36 tests): computeMaxMana, computeRegen,
  computeClickMana, getMeditationBonus, computeEffectiveRegenForDisplay

Total: 163 new tests, all passing. No existing tests broken.

src/lib/game/__tests__/floor-utils.test.ts

@@ -0,0 +1,84 @@
+import { describe, it, expect } from 'vitest';
+import { getFloorMaxHP, getFloorElement } from '../utils/floor-utils';
+
+// ─── getFloorMaxHP ────────────────────────────────────────────────────────────
+
+describe('getFloorMaxHP', () => {
+  it('should return positive HP for floor 1', () => {
+    expect(getFloorMaxHP(1)).toBeGreaterThan(0);
+  });
+
+  it('should return base HP of 100 + scaling for floor 1', () => {
+    // baseHP=100 + floorScaling=50 + exponentialScaling=1 = 151
+    expect(getFloorMaxHP(1)).toBe(151);
+  });
+
+  it('should scale with floor number', () => {
+    const hp1 = getFloorMaxHP(1);
+    const hp5 = getFloorMaxHP(5);
+    const hp10 = getFloorMaxHP(10);
+    expect(hp5).toBeGreaterThan(hp1);
+    expect(hp10).toBeGreaterThan(hp5);
+  });
+
+  it('should return much higher HP for guardian floors', () => {
+    const hp9 = getFloorMaxHP(9);
+    const hp10 = getFloorMaxHP(10); // Ignis Prime guardian
+    expect(hp10).toBeGreaterThan(hp9 * 2);
+  });
+
+  it('should handle high floors', () => {
+    const hp100 = getFloorMaxHP(100);
+    expect(hp100).toBeGreaterThan(0);
+    expect(isFinite(hp100)).toBe(true);
+  });
+
+  it('should be monotonically increasing for non-guardian floors', () => {
+    let prev = getFloorMaxHP(1);
+    for (let f = 2; f <= 9; f++) {
+      const curr = getFloorMaxHP(f);
+      expect(curr).toBeGreaterThan(prev);
+      prev = curr;
+    }
+  });
+});
+
+// ─── getFloorElement ──────────────────────────────────────────────────────────
+
+describe('getFloorElement', () => {
+  it('should return a string element', () => {
+    expect(typeof getFloorElement(1)).toBe('string');
+  });
+
+  it('should return valid element names', () => {
+    const validElements = ['fire', 'water', 'air', 'earth', 'light', 'dark', 'death'];
+    for (let f = 1; f <= 20; f++) {
+      expect(validElements).toContain(getFloorElement(f));
+    }
+  });
+
+  it('should cycle through 7 elements', () => {
+    // Floor 1 and floor 8 should have the same element (cycle of 7)
+    expect(getFloorElement(1)).toBe(getFloorElement(8));
+    expect(getFloorElement(2)).toBe(getFloorElement(9));
+    expect(getFloorElement(7)).toBe(getFloorElement(14));
+  });
+
+  it('should return fire for floor 1', () => {
+    expect(getFloorElement(1)).toBe('fire');
+  });
+
+  it('should return water for floor 2', () => {
+    expect(getFloorElement(2)).toBe('water');
+  });
+
+  it('should return death for floor 7', () => {
+    expect(getFloorElement(7)).toBe('death');
+  });
+
+  it('should handle high floor numbers', () => {
+    const elem = getFloorElement(100);
+    expect(typeof elem).toBe('string');
+    expect(elem.length).toBeGreaterThan(0);
+  });
+});