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/components/game/StudyProgress.tsx

@@ -3,7 +3,7 @@
 import { Button } from '@/components/ui/button';
 import { Progress } from '@/components/ui/progress';
 import { BookOpen, X } from 'lucide-react';
-import { SKILLS_DEF, SPELLS_DEF } from '@/lib/game/constants';
+import { SPELLS_DEF } from '@/lib/game/constants';
 import { formatStudyTime } from '@/lib/game/utils/formatting';
 import type { StudyTarget } from '@/lib/game/types';
 
@@ -21,20 +21,20 @@ export function StudyProgress({
   cancelStudy,
 }: StudyProgressProps) {
   if (!currentStudyTarget) return null;
-  
+
   const target = currentStudyTarget;
   const progressPct = Math.min(100, (target.progress / target.required) * 100);
   const isSkill = target.type === 'skill';
-  const def = isSkill ? SKILLS_DEF[target.id] : SPELLS_DEF[target.id];
+  const def = isSkill ? undefined : SPELLS_DEF[target.id];
   const currentLevel = isSkill ? (skills[target.id] || 0) : 0;
-  
+
   return (
     <div className="p-3 rounded border border-purple-600/50 bg-purple-900/20">
       <div className="flex items-center justify-between mb-2">
         <div className="flex items-center gap-2">
           <BookOpen className="w-4 h-4 text-purple-400" />
           <span className="text-sm font-semibold text-purple-300">
-            {def?.name}
+            {def?.name ?? target.id}
             {isSkill && ` Lv.${currentLevel + 1}`}
           </span>
         </div>