Update documentation after refactoring: AGENTS.md, GAME_BRIEFING.md, skills.md

- Updated AGENTS.md to include store/ directory and clarify store architecture
- Updated GAME_BRIEFING.md Code Architecture section with store/ and legacy store info
- Updated skills.md with skill state management information
- Includes other refactoring changes (store hooks, component updates, etc.)

src/components/game/stats/ManaStatsSection.tsx

@@ -3,7 +3,7 @@
 import { getTierMultiplier } from '@/lib/game/skill-evolution';
 import { hasSpecial, SPECIAL_EFFECTS } from '@/lib/game/effects';
 import { fmt, fmtDec } from '@/lib/game/stores';
-import type { UnifiedEffects } from '@/lib/game/types';
+import type { UnifiedEffects } from '@/lib/game/effects';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { Separator } from '@/components/ui/separator';
 import { Droplet } from 'lucide-react';