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>

docs/guide/getting-started.md

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+# Getting started
+
+Yawn separates the data/render engine from optional scene conventions. Most applications begin with `@yawn/handles`; specialized engines can use `@yawn/core` directly.
+
+## 1. Serve with isolation headers
+
+`SharedArrayBuffer` requires `Cross-Origin-Opener-Policy: same-origin` and `Cross-Origin-Embedder-Policy: require-corp`. The included VitePress server already sends both.
+
+```html
+<canvas id="view"></canvas>
+<script type="module" src="/src/app.ts"></script>
+```
+
+## 2. Start a Scene
+
+```ts
+import { Scene } from "@yawn/handles";
+
+const canvas = document.querySelector<HTMLCanvasElement>("#view")!;
+canvas.width = 1280;
+canvas.height = 720;
+
+const scene = new Scene(canvas, { hdr: true, fps: 60 });
+await scene.ready;
+```
+
+`Scene` initializes conventional SOA rows and loads one clustered-forward HDR render graph. The core itself still starts with only its eight-float `info` row.
+
+## 3. Add a triangle
+
+```ts
+import { Mesh, PBRMaterial } from "@yawn/handles";
+
+const blue = new PBRMaterial(scene, {
+  baseColor: [0.15, 0.55, 1, 1],
+  metallic: 0.15,
+  roughness: 0.4,
+});
+await blue.ready;
+
+const triangle = new Mesh(scene, {
+  material: blue,
+  vertexData: {
+    positions: [-0.7, -0.6, 0, 0.7, -0.6, 0, 0, 0.72, 0],
+    indices: [0, 1, 2],
+  },
+});
+await triangle.ready;
+```
+
+Constructors use worker messages only to reserve slots or rebuild the graph. Once `ready` resolves, ordinary property writes mutate shared memory.
+
+<Playground />
+
+<script setup>
+import Playground from "../.vitepress/Playground.vue";
+</script>