refactor: resolve structural inconsistencies and dead code

- Fix broken barrel exports in components/game/index.ts
- Remove skill system from stores (gameStore, gameActions, gameLoopActions, gameHooks, craftingStore, combat)
- Remove skill system from components (page.tsx, LeftPanel, StatsTab, SpellsTab, EnchantmentDesigner, EnchantmentPreparer, GameContext/Provider)
- Delete dead code: stats/ directory, attunements/ directory, layout/ Header+TabBar, shared/ StudyProgress+UpgradeDialog duplicates, effects.ts.fix, study-slice.ts, navigation-slice.ts
- Delete legacy store/ and store-modules/ directories, redirect remaining callers
- Merge root formatting.ts into utils/formatting.ts
- Move effects files (dynamic-compute, upgrade-effects, special-effects, upgrade-effects.types) into effects/ directory
- Move debug-context.tsx into components/game/debug/
- Create tabs/index.ts barrel for tab components
- Fix page.tsx lazy imports to use tabs barrel
- Fix all broken import paths across codebase
- Remove SKILLS_DEF and skill-evolution references
- Trim store.ts to under 400 lines by removing dead skill actions

src/lib/game/crafting-design.ts

@@ -4,8 +4,8 @@
 import type { EnchantmentDesign, DesignEffect, AppliedEnchantment } from './types';
 import { calculateEnchantingXP } from './data/attunements';
 import { ENCHANTMENT_EFFECTS, calculateEffectCapacityCost } from './data/enchantment-effects';
-import { hasSpecial, SPECIAL_EFFECTS } from './special-effects';
-import { computeEffects } from './upgrade-effects';
+import { hasSpecial, SPECIAL_EFFECTS } from './effects/special-effects';
+import { computeEffects } from './effects/upgrade-effects';
 import { EQUIPMENT_TYPES, type EquipmentCategory } from './data/equipment';
 
 // ─── Design Creation & Calculation ──────────────────────────────────────────