refactor: remove memory slot system and Memories section from PrestigeTab

- Remove deepMemory prestige upgrade from constants/prestige.ts
- Remove Memory interface from types.ts
- Remove memorySlots, memories, addMemory, removeMemory, clearMemories from prestigeStore.ts
- Remove deepMemory/memory references from gameLoopActions.ts
- Remove MemoriesCard component and its usage from PrestigeTab.tsx
- Remove memorySlots display from LoopStatsSection.tsx
- Update tests: store-actions-combat-prestige.test.ts, PrestigeTab.test.ts, tick-integration.test.ts

The memory slot system was fully wired but had no gameplay mechanic — addMemory()
was never called outside tests. This removes dead code across 9 files.

src/lib/game/constants/prestige.ts

@@ -4,7 +4,6 @@ import type { PrestigeDef } from '../types';
 export const PRESTIGE_DEF: Record<string, PrestigeDef> = {
   manaWell:     { name: "Mana Well",     desc: "+500 starting max mana",     max: 5,  cost: 500 },
   manaFlow:     { name: "Mana Flow",     desc: "+0.5 regen/sec permanently", max: 10, cost: 750 },
-  deepMemory:   { name: "Deep Memory",   desc: "+1 memory slot",             max: 5,  cost: 1000 },
   insightAmp:   { name: "Insight Amp",   desc: "+25% insight gain",          max: 4,  cost: 1500 },
   spireKey:     { name: "Spire Key",     desc: "Start at floor +2",          max: 5,  cost: 4000 },
   temporalEcho: { name: "Temporal Echo", desc: "+10% mana generation",       max: 5,  cost: 3000 },