feat: remove Spells tab UI

- Remove Spells tab trigger from TabTriggers in page.tsx
- Remove TabsContent value='spells' block in page.tsx
- Remove lazy import of SpellsTab in page.tsx
- Change default activeTab from 'spells' to 'disciplines'
- Remove SpellsTab re-export from tabs/index.ts
- Remove SpellsTab re-export from game/index.ts
- Delete src/components/game/tabs/SpellsTab.tsx

Spell data (SPELLS_DEF, spells store state) preserved - spells still exist as enchantments.

src/components/game/index.ts

@@ -2,7 +2,6 @@
 // Re-exports all game tab components for cleaner imports
 
 // Tab components (consolidated in tabs/ subfolder)
-export { SpellsTab } from './tabs/SpellsTab';
 export { StatsTab } from './tabs/StatsTab';
 
 // UI components