Add tutorial docs and interactive playgrounds

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

docs/packages/gltf-import.md

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+# glTF import worker
+
+`@yawn/gltf-import` keeps parsing and bulk upload off the renderer command channel. It fetches a `.gltf` or `.glb` URL in a dedicated worker and writes a format-neutral packet directly into shared memory.
+
+## Load a scene
+
+```js
+import { GltfImporter } from "@yawn/gltf-import";
+
+const importer = new GltfImporter(core);
+try {
+  const result = await importer.load("/models/level.glb");
+  console.log(result.meshes, result.materials, result.bounds);
+} finally {
+  importer.dispose();
+}
+```
+
+The import handshake is:
+
+1. The import worker fetches and measures the asset packet.
+2. Core allocates a fixed `upload.renderData` shared array.
+3. The import worker writes packet bytes into that SAB.
+4. Core receives only the array ID and byte count, then installs render data.
+
+No GLB payload is copied through the renderer's message queue.
+
+<Playground
+  id="gltf-worker"
+  title="Worker-side glTF import"
+  description="A generated GLB is fetched through an object URL and committed from shared upload memory."
+/>
+
+## Camera framing
+
+Import frames the canonical `camera.state` row from scene bounds by default. Select an exterior or interior framing policy, or preserve the current camera.
+
+```js
+await importer.load(url, { framing: "exterior" });
+await importer.load(url, { framing: "interior" });
+await importer.load(url, { framing: false });
+```
+
+Framing is an addon behavior implemented as a shared camera-row write. It is not a camera subsystem in core.
+
+## Wrap the result when useful
+
+Import returns protocol descriptors. Less technical consumers can turn those descriptors into generation-safe objects.
+
+```js
+import { MeshHandles, MaterialHandles } from "@yawn/mesh-handles";
+
+const meshes = new MeshHandles(core).fromImportedScene(result);
+const materials = new MaterialHandles(core).fromImportedScene(result);
+```