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/app/page.tsx

@@ -33,7 +33,6 @@ import { LeftPanel } from './components/LeftPanel';
 
 // Lazy load tab components
 const DisciplinesTab = lazy(() => import('@/components/game/tabs').then(m => ({ default: m.DisciplinesTab })));
-const SpellsTab = lazy(() => import('@/components/game/tabs').then(m => ({ default: m.SpellsTab })));
 const StatsTab = lazy(() => import('@/components/game/tabs').then(m => ({ default: m.StatsTab })));
 const DebugTab = lazy(() => import('@/components/game/tabs').then(m => ({ default: m.DebugTab })));
 const AchievementsTab = lazy(() => import('@/components/game/tabs').then(m => ({ default: m.AchievementsTab })));
@@ -114,7 +113,6 @@ function useGameDerivedStats() {
 function TabTriggers() {
   return (
     <TabsList className="flex flex-wrap gap-1 w-full mb-4 h-auto">
-      <TabsTrigger value="spells" className="text-xs px-2 py-1">🔮 Spells</TabsTrigger>
       <TabsTrigger value="stats" className="text-xs px-2 py-1">📊 Stats</TabsTrigger>
       <TabsTrigger value="disciplines" className="text-xs px-2 py-1">📚 Disciplines</TabsTrigger>
       <TabsTrigger value="debug" className="text-xs px-2 py-1">🐛 Debug</TabsTrigger>
@@ -145,7 +143,7 @@ function LazyTab({ name, children }: { name: string; children: React.ReactNode }
 // ─── Main Game Component ─────────────────────────────────────────────────────
 
 export default function ManaLoopGame() {
-  const [activeTab, setActiveTab] = useState('spells');
+  const [activeTab, setActiveTab] = useState('disciplines');
 
   useGameLoop();
 
@@ -211,7 +209,6 @@ export default function ManaLoopGame() {
               <Tabs value={activeTab} onValueChange={setActiveTab}>
                 <TabTriggers />
 
-                <TabsContent value="spells"><LazyTab name="spells"><SpellsTab /></LazyTab></TabsContent>
                 <TabsContent value="stats"><LazyTab name="stats"><StatsTab /></LazyTab></TabsContent>
                 <TabsContent value="disciplines"><LazyTab name="disciplines"><DisciplinesTab /></LazyTab></TabsContent>
                 <TabsContent value="debug"><LazyTab name="debug"><DebugTab /></LazyTab></TabsContent>