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/debug/ElementDebug.tsx

@@ -52,7 +52,7 @@ export function ElementDebug() {
                     className="mt-2"
                     onClick={() => handleUnlockElement(id)}
                   >
-                    <Unlock className="w-3 h-3 mr-1" /> Unlock
+                    <Lock className="w-3 h-3 mr-1" /> Unlock
                   </Button>
                 )}
                 {elem.unlocked && (