Add FxNode render graph playground

Add persistent render graph loadouts, grouped node authoring, code-appending apply behavior, explicit playground lighting, and resilient worker startup.

Amp-Thread-ID: https://ampcode.com/threads/T-01a033d4-0e44-708e-af0e-6166283416ff
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

docs/guide/lights.md

@@ -8,6 +8,7 @@ const point = new PointLight(scene, {
   color: [1, 0.25, 0.05],
   intensity: 20,
   range: 8,
+  radius: 0.5, // Softens the specular footprint like a small spherical emitter.
 });
 
 const sun = new DirectionalLight(scene, {
@@ -16,7 +17,10 @@ const sun = new DirectionalLight(scene, {
   intensity: 3,
 });
 
-const fill = new AmbientLight(scene, { color: [0.1, 0.2, 0.4], intensity: 0.2 });
+const fill = new AmbientLight(scene, {
+  color: [0.1, 0.2, 0.4],
+  intensity: 0.2,
+});
 await Promise.all([point.ready, sun.ready, fill.ready]);
 ```