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/core.md

@@ -0,0 +1,44 @@
+# Core boundary
+
+`@yawn/core` deliberately contains no scene types and no WGSL. It owns two things:
+
+1. a 64-byte-aligned arena of named f32/u32/i32 SOA rows in one `SharedArrayBuffer`;
+2. render-graph compilation, up-front WebGPU loadouts, transient resource aliasing, render bundles, and the paced render loop.
+
+```text
+infrequent worker messages                  hot shared mutations
+┌──────────────────────────────┐            ┌──────────────────────┐
+│ create/delete rows           │            │ transforms           │
+│ allocate/delete object slot  │            │ cameras/materials    │
+│ compile/switch graph         │            │ lights/app data      │
+│ play/pause/set FPS           │            │ info.skipRender      │
+└──────────────┬───────────────┘            └──────────┬───────────┘
+               └─────────────────┬─────────────────────┘
+                                 ▼
+                        ┌─────────────────┐
+                        │ Rust/WASM core  │
+                        └─────────────────┘
+```
+
+## Use core directly
+
+```ts
+import { YawnCore } from "@yawn/core";
+
+const core = new YawnCore(canvas, { arenaBytes: 64 * 1024 * 1024 });
+await core.ready;
+
+const values = await core.createRows({
+  name: "application.values",
+  rows: 1024,
+  stride: 16,
+  format: "f32",
+});
+
+const id = await core.allocateObject("application.values");
+values.row(id).set([1, 2, 3, 4]);
+```
+
+Graph frontends serialize plain data to `(yawn-graph 1 ...)`. Named `after` edges preserve DAG fan-out; Rust sorts passes, detects cycles, culls unused declarations, plans compatible transient lifetimes, and allocates the active loadout.
+
+The `Scene` addon is one such frontend. It is replaceable and has no privileged core API.