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/compute.md

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+# Compute passes
+
+Compute shaders are graph data, not core code. Declare the shared rows/resources a shader needs and attach the pass to `Scene`.
+
+```ts
+const velocity = await scene.ensureRows("velocity", 4096, 16, "f32");
+
+const simulation = new ComputePass({
+  id: "integrate",
+  code: `
+    @group(0) @binding(0)
+    var<storage, read_write> velocity: array<vec4<f32>>;
+
+    @compute @workgroup_size(64)
+    fn main(@builtin(global_invocation_id) id: vec3<u32>) {
+      if (id.x < arrayLength(&velocity)) {
+        velocity[id.x].y -= 0.001;
+      }
+    }
+  `,
+  buffers: [{ id: "velocity", array: "velocity", usage: ["storage"] }],
+  bindings: [{ group: 0, binding: 0, resource: "velocity" }],
+  dispatch: [64, 1, 1],
+});
+
+await scene.addComputePass(simulation);
+```
+
+<Playground example="compute" />
+
+The graph DAG places an unqualified custom compute pass after light clustering and makes forward rendering depend on all custom compute passes. Use `after` to specify other dependencies.
+
+```ts
+await simulation.update({ dispatch: [128, 1, 1] });
+await scene.removeComputePass(simulation);
+```
+
+Both operations are infrequent graph/loadout messages. Existing source row changes are direct SAB writes.
+
+<script setup>
+import Playground from "../.vitepress/Playground.vue";
+</script>