feat: implement DoT/debuff runtime system (spec §6, AC-12, AC-13)

- Add ActiveEffect, EffectType types to game.ts; activeEffects + effectiveArmor on EnemyState
- Add SpellOnHitEffect + onHitEffect field to SpellDefinition
- Wire onHitEffect to fire (burn), death (curse), lightning (armor_corrode), frost (freeze), soul (bypassArmor burn)
- Add applyOnHitEffect() — applies on-hit effect on successful spell hit (spec §6.2)
- Add processDoTPhase() — ticks all active effects after weapon/golem attacks (spec §6.3)
- Add bypassArmor/bypassBarrier support in applyEnemyDefenses() (AC-13)
- Export standalone applyEnemyDefenses from combat-tick.ts for DoT pipeline
- Split DoT runtime into separate dot-runtime.ts (135 lines) to keep combat-actions.ts under 400 lines
- Update all enemy generation sites with activeEffects/effectiveArmor defaults
- Fix test helpers for new required fields

All 921 tests pass (45 test files)

src/lib/game/stores/combat-actions.ts

@@ -5,8 +5,10 @@
 import { SPELLS_DEF, HOURS_PER_TICK } from '../constants';
 import { getGuardianForFloor } from '../data/guardian-encounters';
 import type { CombatStore, CombatState } from './combat-state.types';
-import type { SpellState } from '../types';
+import type { SpellState, EnemyState } from '../types';
+import { applyOnHitEffect, processDoTPhase } from './dot-runtime';
 import type { ActiveGolem } from '../types';
+import type { SpellOnHitEffect } from '../types/spells';
 import { getFloorMaxHP, getFloorElement, getMultiElementBonus, calcDamage, canAffordSpellCost, deductSpellCost } from '../utils';
 import { computeDisciplineEffects } from '../effects/discipline-effects';
 import { processGolemMaintenance, processGolemAttacks } from './golem-combat-actions';
@@ -65,6 +67,14 @@ export function processCombatTick(
   signedPacts: number[],
   golemancyState: { activeGolems: ActiveGolem[] },
   golemApplyDamageToRoom: (dmg: number) => { floorHP: number; floorMaxHP: number; roomCleared: boolean },
+  applyEnemyDefenses: (
+    dmg: number,
+    enemy: EnemyState | null,
+    roomType: string,
+    addLog: (msg: string) => void,
+    bypassArmor?: boolean,
+    bypassBarrier?: boolean,
+  ) => number,
 ): CombatTickResult {
   const state = get();
   const logMessages: string[] = [];
@@ -177,6 +187,9 @@ export function processCombatTick(
       castProgress -= 1;
       safetyCounter++;
 
+      // Apply on-hit effect (DoT/debuff) to enemy (spec §6.2)
+      applyOnHitEffect(get, set, spellId, logMessages);
+
       // Check if room/floor is cleared
       if (floorHP <= 0) {
         const guardian = getGuardianForFloor(currentFloor);
@@ -302,6 +315,24 @@ export function processCombatTick(
       currentFloor = postGolemState.currentFloor;
     }
 
+    // ─── DoT/Debuff tick processing (spec §6.3) ──────────────────────────
+    // Process after all weapon/golem attacks
+    if (floorHP > 0) {
+      const doTDamage = processDoTPhase(get, set, applyEnemyDefenses, logMessages);
+      floorHP = Math.max(0, floorHP - doTDamage);
+
+      // Check if DoT cleared the room
+      if (floorHP <= 0) {
+        const guardian = getGuardianForFloor(currentFloor);
+        onFloorCleared(currentFloor, !!guardian);
+        get().advanceRoomOrFloor();
+        const newState = get();
+        currentFloor = newState.currentFloor;
+        floorMaxHP = newState.floorMaxHP;
+        floorHP = newState.floorHP;
+      }
+    }
+
     const newMaxFloorReached = Math.max(state.maxFloorReached, currentFloor);
 
     return {