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/components/game/tabs/StatsTab/LoopStatsSection.tsx

@@ -14,7 +14,6 @@ export function LoopStatsSection() {
   const maxFloorReached = useCombatStore((s) => s.maxFloorReached);
   const totalManaGathered = useManaStore((s) => s.totalManaGathered);
   const loopCount = usePrestigeStore((s) => s.loopCount);
-  const memorySlots = usePrestigeStore((s) => s.memorySlots);
 
   const spellsLearned = Object.values(spells || {}).filter((s: SpellState) => s.learned).length;
 
@@ -46,7 +45,7 @@ export function LoopStatsSection() {
           </div>
         </div>
         <Separator className="bg-[var(--border-subtle)] my-3" />
-        <div className="grid grid-cols-2 md:grid-cols-4 gap-4">
+        <div className="grid grid-cols-2 md:grid-cols-3 gap-4">
           <div className="p-3 bg-[var(--bg-sunken)]/50 rounded text-center">
             <div className="text-xl font-bold text-[var(--text-secondary)] game-mono">{spellsLearned}</div>
             <div className="text-xs" style={{ color: 'var(--text-muted)' }}>Spells Learned</div>
@@ -55,10 +54,6 @@ export function LoopStatsSection() {
             <div className="text-xl font-bold text-[var(--text-secondary)] game-mono">{fmt(totalManaGathered)}</div>
             <div className="text-xs" style={{ color: 'var(--text-muted)' }}>Total Mana Gathered</div>
           </div>
-          <div className="p-3 bg-[var(--bg-sunken)]/50 rounded text-center">
-            <div className="text-xl font-bold text-[var(--text-secondary)] game-mono">{memorySlots}</div>
-            <div className="text-xs" style={{ color: 'var(--text-muted)' }}>Memory Slots</div>
-          </div>
         </div>
       </CardContent>
     </Card>