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/index.md

@@ -0,0 +1,35 @@
+---
+layout: home
+
+hero:
+  name: Yawn
+  text: Build the graph. Share the data.
+  tagline: A worker-native WebGPU renderer where infrequent lifecycle commands use messages and hot render data lives in SIMD-aligned shared memory.
+  actions:
+    - theme: brand
+      text: Build your first scene
+      link: /guide/first-scene
+    - theme: alt
+      text: Open the playground
+      link: /../playground/
+
+features:
+  - title: One graph boundary
+    details: JSO, a fluent builder, and FXNode all export the same immutable DAG AST and S-expression wire format.
+  - title: Shared render data
+    details: Meshes, instances, camera state, materials, and user columns use aligned SOA rows backed by shared WASM memory.
+  - title: External programs
+    details: WGSL, render pipelines, and compute passes travel with a graph loadout; core ships no scene shader.
+  - title: Worker-native
+    details: The same core client runs on the browser main thread or another worker through a Worker-like endpoint.
+  - title: Up-front loadouts
+    details: Graph compilation culls dead work, aliases compatible transients, coalesces passes, and prepares resources before activation.
+  - title: Optional conveniences
+    details: glTF import, mesh handles, material properties, camera controls, and picking stay in focused addons.
+---
+
+<Playground
+  id="first-scene"
+  title="Your first Yawn scene"
+  description="The preview imports procedural glTF through a worker, activates a graph, and renders shared instance data."
+/>