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/app/components/LeftPanel.tsx

@@ -10,7 +10,6 @@ import { DebugName } from '@/lib/game/debug-context';
 import type { GameStore } from '@/lib/game/store';
 import { computeMaxMana, computeClickMana, getMeditationBonus } from '@/lib/game/store';
 import { getUnifiedEffects } from '@/lib/game/effects';
-import { useGameLoop } from '@/lib/game/stores/gameHooks';
 
 interface LeftPanelProps {
   store: GameStore;