Enabled switch, text assets, mouse input and the jump-and-run example game

Engine additions that the example game needed:
- `enabled` as a shared property of every placeable asset (default on, an
  override on the scene object). A switched-off object is not drawn, does not
  collide and its behavior does not run - and neither does anything parented
  below it. Disabled objects are now hidden in the scene view as well, so the
  editor shows what the game shows; they stay in the hierarchy panel, which is
  where they are selected and switched back on.
- Asset type `text` (text, fontSize, color, align), rendered in scene and game.
- Pointer input in the game view: `On click`, `Mouse position`, `Mouse button`,
  `Is hovered`, hit-tested against colliders, else sprite/text footprints.
- New nodes: Set/Is enabled, Set text, Is asset, Name of, Equals, To text,
  Join text, Floor/Ceil/Round, Modulo, Random, Time, Restart game.

Tooling: shared CDP harness (tools/harness.mjs), central project registry with
a guard that keeps destructive scripts off the playground (tools/projects.mjs),
plus smoke suites for the demo scene and the jump-and-run game.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/core/resolve.test.ts

@@ -15,7 +15,7 @@ describe('PropertySchema', () => {
   });
 
   it('provides defaults for every key', () => {
-    expect(defaultsFor('sprite')).toEqual({ width: 100, height: 100, color: 0xe0553f });
+    expect(defaultsFor('sprite')).toEqual({ enabled: true, width: 100, height: 100, color: 0xe0553f });
   });
 
   it('coerces values against the definition', () => {
@@ -33,14 +33,14 @@ describe('resolve', () => {
   it('fills asset props with defaults and ignores unknown keys', () => {
     const sprite = buildAsset('sprite', 'Box');
     sprite.props = { width: 50, bogus: 1 };
-    expect(resolveAssetProps(sprite)).toEqual({ width: 50, height: 100, color: 0xe0553f });
+    expect(resolveAssetProps(sprite)).toEqual({ enabled: true, width: 50, height: 100, color: 0xe0553f });
   });
 
   it('applies sparse overrides on top of asset values', () => {
     const sprite = buildAsset('sprite', 'Box');
     sprite.props.color = 0x00ff00;
     const object = createSceneObject('o1', sprite.id, { x: 10, y: 20 });
-    expect(resolveSceneObjectProps(sprite, object)).toEqual({ width: 100, height: 100, color: 0x00ff00 });
+    expect(resolveSceneObjectProps(sprite, object)).toEqual({ enabled: true, width: 100, height: 100, color: 0x00ff00 });
 
     object.overrides.color = 0x0000ff;
     expect(resolveSceneObjectProps(sprite, object).color).toBe(0x0000ff);