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/runtime/Entity.ts

@@ -0,0 +1,19 @@
+import type { AssetType } from '../core/model/AssetTypes';
+import type { PropertyBag } from '../core/model/Properties';
+
+/**
+ * A live instance created from a scene object when Play starts. Holds the *resolved*
+ * property values as mutable runtime state. Systems change entities freely; nothing here
+ * is ever written back to the project model.
+ */
+export interface Entity {
+  id: string;
+  /** Scene object this entity was instantiated from (for selection highlighting). */
+  objectId: string;
+  assetId: string;
+  type: AssetType;
+  name: string;
+  x: number;
+  y: number;
+  props: PropertyBag;
+}