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/lights.md

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+# Clustered lights
+
+The default `Scene` graph runs a clustered compute pass before its HDR forward passes. Light handles write flat rows consumed by that pass.
+
+```ts
+const point = new PointLight(scene, {
+  position: [0, 1, 1],
+  color: [1, 0.25, 0.05],
+  intensity: 20,
+  range: 8,
+});
+
+const sun = new DirectionalLight(scene, {
+  quaternion: [0.2, 0, 0, 0.98],
+  color: [1, 0.95, 0.8],
+  intensity: 3,
+});
+
+const fill = new AmbientLight(scene, { color: [0.1, 0.2, 0.4], intensity: 0.2 });
+await Promise.all([point.ready, sun.ready, fill.ready]);
+```
+
+<Playground example="lights" />
+
+## Rectangles and spots
+
+```ts
+const panel = new RectAreaLight(scene, {
+  position: [0, 2, 0],
+  width: 2,
+  height: 0.5,
+  intensity: 12,
+});
+
+const spot = new SpotLight(scene, {
+  position: [0, 1, 1],
+  innerAngle: 0.25,
+  outerAngle: 0.6,
+  range: 15,
+});
+```
+
+The rectangle handle selects the default graph's linearly transformed cosine (`ltc`) path. Position, orientation, intensity, angles, and colors remain direct SAB mutations after allocation.
+
+<script setup>
+import Playground from "../.vitepress/Playground.vue";
+</script>