cleanup: delete computed-stats.ts shim and store/index.ts

- Delete src/lib/game/computed-stats.ts (root-level re-export shim)
- Delete src/lib/game/store/index.ts (nothing imports from it)
- Update __tests__/computed-stats.test.ts to import from ../utils instead
- Clean up craftingStore.ts imports (remove unused useGameStore, CraftingApply)

Typecheck and lint pass (pre-existing DisciplinesTab.tsx errors unchanged)

src/lib/game/stores/index.ts

@@ -11,9 +11,6 @@ export type { PrestigeState } from './prestigeStore';
 export { useManaStore, makeInitialElements } from './manaStore';
 export type { ManaState } from './manaStore';
 
-export { useSkillStore } from './skillStore';
-export type { SkillState } from './skillStore';
-
 export { useCombatStore, makeInitialSpells } from './combatStore';
 export type { CombatState } from './combatStore';