Initial commit: Game Maker phase 1

Canvas-only 2D game editor/runtime built on PixiJS v8 + Vite + TypeScript.

- core: asset model (Scene/Camera/Sprite), scene objects with sparse
  overrides, property schema + resolve, command stack (undo/redo),
  serialization and project store interface (16 unit tests)
- ui: custom in-canvas widget toolkit (panels, fields, color picker,
  list/scroll, popup) with a hidden <input> keyboard bridge
- editor: asset/hierarchy panels, schema-driven inspector, toolbar
- viewport: box rendering, camera frame, selection gizmo, drag/zoom/pan
- runtime: world/entity instantiation for play mode, input, camera follow
- api: PHP JSON project store with revision counter (409 on conflict)
- tools: CDP-based e2e smoke test

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/core/model/SceneObject.ts

@@ -0,0 +1,19 @@
+import type { PropertyBag, Vec2 } from './Properties';
+
+/**
+ * An asset placed inside a scene. It links to the asset by id, owns a position
+ * (assets have none) and may override individual asset properties. Overrides are
+ * sparse: only keys the user changed are stored; everything else follows the asset.
+ */
+export interface SceneObject {
+  id: string;
+  assetId: string;
+  /** Optional display name; falls back to the asset name when empty. */
+  name: string;
+  position: Vec2;
+  overrides: PropertyBag;
+}
+
+export function createSceneObject(id: string, assetId: string, position: Vec2): SceneObject {
+  return { id, assetId, name: '', position: { x: position.x, y: position.y }, overrides: {} };
+}