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/gameStore.ts

@@ -28,6 +28,7 @@ import { buildGolemCombatPipeline } from './pipelines/golem-combat';
 import type { TickContext, TickWrites } from './tick-pipeline';
 import type { GameCoordinatorState } from './gameStore.types';
 import type { EnemyState } from '../types';
+import { applyEnemyDefenses as applyEnemyDefensesFromPipeline } from './pipelines/combat-tick';
 
 export interface GameCoordinatorStore extends GameCoordinatorState {
   tick: () => void;
@@ -309,6 +310,9 @@ export const useGameStore = create<GameCoordinatorStore>()(
               ctx.prestige.signedPacts,
               { activeGolems: golemPipeline.activeGolems },
               golemPipeline.golemApplyDamageToRoom,
+              (dmg, enemy, roomType, addLogFn, bypassArmor, bypassBarrier) => applyEnemyDefensesFromPipeline(
+                dmg, enemy, roomType, addLogFn, bypassArmor, bypassBarrier,
+              ),
             );
             rawMana = combatResult.rawMana;
             elements = combatResult.elements;