update: add agent.md + skills

.agent/skills/memory.md

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+# Skill — GPU Memory Management
+
+## Principle
+
+Dispose only what you own. Never blindly traverse and dispose shared or cached assets.
+
+## What to dispose
+
+| Resource                           | When to dispose                      |
+| ---------------------------------- | ------------------------------------ |
+| Custom `THREE.ShaderMaterial`      | When the component using it unmounts |
+| `THREE.WebGLRenderTarget`          | When the pass or effect is destroyed |
+| Manually created `THREE.Geometry`  | When no longer needed                |
+| Manually created `THREE.Texture`   | When no longer needed                |
+| Cloned scenes with owned materials | When the clone is removed            |
+
+## What NOT to dispose
+
+| Resource                         | Why                                             |
+| -------------------------------- | ----------------------------------------------- |
+| GLTF scenes loaded via `useGLTF` | drei caches them — disposing breaks other users |
+| Textures loaded via `useTexture` | drei caches them — same reason                  |
+| Shared materials from a GLTF     | Other instances may reference them              |
+
+## Dispose utility
+
+```ts
+// src/utils/Dispose.ts
+import * as THREE from "three";
+
+export class Dispose {
+  static material(material: THREE.Material): void {
+    for (const value of Object.values(material)) {
+      if (value instanceof THREE.Texture) {
+        value.dispose();
+      }
+    }
+    material.dispose();
+  }
+
+  static mesh(mesh: THREE.Mesh): void {
+    mesh.geometry?.dispose();
+    const materials = Array.isArray(mesh.material)
+      ? mesh.material
+      : [mesh.material];
+    for (const mat of materials) {
+      if (mat) this.material(mat);
+    }
+  }
+
+  static renderTarget(rt: THREE.WebGLRenderTarget): void {
+    rt.texture.dispose();
+    rt.dispose();
+  }
+}
+```
+
+## Usage in React components
+
+```tsx
+useEffect(() => {
+  const material = new THREE.ShaderMaterial({ vertexShader, fragmentShader });
+  meshRef.current.material = material;
+
+  return () => {
+    Dispose.material(material);
+  };
+}, []);
+```
+
+## Usage in managers
+
+```ts
+destroy(): void {
+  if (this.renderTarget) {
+    Dispose.renderTarget(this.renderTarget)
+    this.renderTarget = null
+  }
+  SomeManager._instance = null
+}
+```
+
+## Rules
+
+- Every `useEffect` that creates a GPU resource must return a cleanup that disposes it
+- Every manager `destroy()` must dispose its owned GPU resources
+- Never call `.dispose()` on assets returned by drei loaders (`useGLTF`, `useTexture`)
+- When in doubt, don't dispose — a small leak is better than a crash from disposing shared resources