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/store.test.ts

@@ -1,9 +1,8 @@
 /**
  * Unit Tests for Mana Loop Game Logic
- * 
+ *
  * This file contains comprehensive tests for the game's core mechanics.
- * Updated for the new skill system with tiers and upgrade trees.
- * 
+ *
  * This file has been refactored - individual test suites have been moved to
  * the store-tests/ directory. This file re-exports all tests for convenience.
  */
@@ -19,6 +18,3 @@ export * from './store-tests/study-speed.test';
 export * from './store-tests/game-constants.test';
 export * from './store-tests/element-recipes.test';
 export * from './store-tests/integration.test';
-export * from './store-tests/skill-evolution.test';
-export * from './store-tests/individual-skills.test';
-export * from './store-tests/skill-requirements.test';