update: add agent.md + skills

.agent/skills/managers.md

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+# Skill — Singleton Managers
+
+## Pattern
+
+Every manager follows the exact same singleton structure:
+
+```ts
+export class SomeManager {
+  private static _instance: SomeManager | null = null;
+
+  static getInstance(): SomeManager {
+    if (!SomeManager._instance) {
+      SomeManager._instance = new SomeManager();
+    }
+    return SomeManager._instance;
+  }
+
+  private constructor() {
+    // init logic
+  }
+
+  destroy(): void {
+    // cleanup logic
+    SomeManager._instance = null;
+  }
+}
+```
+
+## Managers in this project
+
+| Manager            | File                                   | Role                                                                                                       |
+| ------------------ | -------------------------------------- | ---------------------------------------------------------------------------------------------------------- |
+| `GameManager`      | `src/stateManager/GameManager.ts`      | Single source of truth. Owns phase, zone, mission, input lock, dialogue. Has `subscribe()` + `getState()`. |
+| `CinematicManager` | `src/stateManager/CinematicManager.ts` | GSAP timelines. Locks/unlocks input via GameManager.                                                       |
+| `AudioManager`     | `src/stateManager/AudioManager.ts`     | Music, SFX, spatial audio. Reads phase from GameManager.                                                   |
+| `ZoneManager`      | `src/stateManager/ZoneManager.ts`      | Zone entry/exit detection, LOD triggers. Notifies GameManager of zone changes.                             |
+
+## GameManager is the orchestrator
+
+```ts
+export class GameManager {
+  cinematic!: CinematicManager;
+  audio!: AudioManager;
+  zone!: ZoneManager;
+
+  private constructor() {
+    this.cinematic = CinematicManager.getInstance();
+    this.audio = AudioManager.getInstance();
+    this.zone = ZoneManager.getInstance();
+  }
+}
+```
+
+Components and hooks access other managers **through GameManager only**:
+
+```ts
+// Correct
+GameManager.getInstance().cinematic.play("intro");
+
+// Wrong — never import sub-managers directly in components
+CinematicManager.getInstance().play("intro");
+```
+
+## Subscribe pattern (GameManager only)
+
+```ts
+private listeners = new Set<() => void>()
+
+subscribe(listener: () => void): () => void {
+  this.listeners.add(listener)
+  return () => this.listeners.delete(listener)
+}
+
+private emit(): void {
+  this.listeners.forEach((cb) => cb())
+}
+```
+
+Every `set*()` method calls `this.emit()` to notify subscribers.
+
+## React bridge hook
+
+```ts
+// hooks/useGameState.ts
+export function useGameState() {
+  const game = GameManager.getInstance();
+  const [state, setState] = useState(game.getState());
+
+  useEffect(() => {
+    return game.subscribe(() => setState({ ...game.getState() }));
+  }, [game]);
+
+  return state;
+}
+```
+
+## Rules
+
+- Max 4 managers total
+- Only `GameManager` holds durable state with `subscribe()`
+- Other managers are side-effect handlers — they do not store persistent state
+- Always call `destroy()` on cleanup (App unmount)
+- Never create manager instances with `new` — always use `.getInstance()`