Replace addons with conventional handles

Provide the single-loadout Scene API, SAB-backed meshes, cameras, materials, lights, workers, post effects, and tutorial playgrounds. Batch matching row growth so active GPU loadouts refresh once.

Amp-Thread-ID: https://ampcode.com/threads/T-01a01380-b478-77d0-84a0-102880a5c5ae
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

addons/handles/src/materials/ShaderMaterial.ts

@@ -0,0 +1,48 @@
+import type { Scene } from "../Scene";
+
+export type ShaderMaterialOptions = {
+  code: string;
+  vertexEntry?: string;
+  fragmentEntry?: string;
+};
+
+/** User WGSL represented as a material handle; registration rebuilds the Scene graph loadout. */
+export class ShaderMaterial {
+  readonly scene: Scene;
+  id = -1;
+  code: string;
+  vertexEntry: string;
+  fragmentEntry: string;
+  readonly ready: Promise<this>;
+  #disposed = false;
+
+  constructor(scene: Scene, options: ShaderMaterialOptions) {
+    if (!options?.code) throw new TypeError("ShaderMaterial code is required");
+    this.scene = scene;
+    this.code = options.code;
+    this.vertexEntry = options.vertexEntry ?? "vertex";
+    this.fragmentEntry = options.fragmentEntry ?? "fragment";
+    this.ready = scene.allocateMaterial().then(async (id) => {
+      this.id = id;
+      await scene.registerShader(this);
+      return this;
+    });
+  }
+
+  async update(options: Partial<ShaderMaterialOptions>) {
+    await this.ready;
+    if (options.code !== undefined) this.code = options.code;
+    if (options.vertexEntry !== undefined) this.vertexEntry = options.vertexEntry;
+    if (options.fragmentEntry !== undefined) this.fragmentEntry = options.fragmentEntry;
+    await this.scene.registerShader(this);
+    return this;
+  }
+
+  async dispose() {
+    await this.ready;
+    if (this.#disposed) return;
+    this.#disposed = true;
+    await this.scene.unregisterShader(this.id);
+    await this.scene.core.deleteObject("materials", this.id);
+  }
+}