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/cameras.md

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+# Cameras and controls
+
+Every camera allocates a generic `cameras` slot and a transform node. Projection, lens, controller state, and transforms are direct SAB rows after construction.
+
+## Shared lens and projection controls
+
+```ts
+const camera = new Camera(scene, {
+  fov: Math.PI / 3,
+  near: 0.05,
+  far: 2000,
+  focalLength: 50,
+  aperture: 2.8,
+  focusDistance: 8,
+});
+await camera.ready;
+
+camera.projection = "orthographic";
+camera.orthoSize = 12;
+camera.projection = "perspective";
+```
+
+`fov`, `aspect`, `near`, `far`, `orthoSize`, `focalLength`, `aperture`, `focusDistance`, and `sensorWidth` all write the camera's shared row.
+
+## Arc rotate
+
+```ts
+const orbit = new ArcRotateCamera(scene, {
+  alpha: 0,
+  beta: Math.PI / 3,
+  radius: 6,
+  target: mesh,
+  controls: {
+    element: canvas,
+    pointer: true,      // left orbit, right pan, wheel zoom
+    controller: true,  // sticks + triggers
+  },
+});
+await orbit.ready;
+```
+
+## Free spectator camera
+
+```ts
+const free = new FreeCamera(scene, {
+  position: [0, 1, 5],
+  controls: {
+    element: canvas,
+    keyboard: true,    // WASD + Space/Ctrl
+    pointer: true,     // click for pointer lock, mouse to look
+    controller: true,
+    speed: 6,
+  },
+});
+await free.ready;
+```
+
+## Follow a character
+
+```ts
+const follow = new FollowCamera(scene, {
+  target: player,
+  distance: 5,
+  height: 1.8,
+  smoothing: 0.12,
+});
+await follow.ready;
+
+follow.target = anotherPlayer;
+follow.distance = 7;
+follow.stop();
+follow.start();
+```
+
+The input and follow loops never post camera updates to core: they read and mutate the same camera, position, and quaternion rows that any other worker can use.