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>

src/core/graph/NodeRegistry.ts

@@ -1,4 +1,5 @@
 import type { PropertyBag, PropertyValue } from '../model/Properties';
+import { enabledAlongChain } from '../properties/enabled';
 import type { PropertyDef } from '../properties/PropertySchema';
 import type { PortType } from './Graph';
 
@@ -11,6 +12,8 @@ export type Value = PropertyValue | EntityHandle | null;
  */
 export interface EntityHandle {
   id: string;
+  /** Asset this entity was instantiated from (what `Is asset` compares against). */
+  assetId: string;
   name: string;
   /** Position local to `parent` (world position for top-level entities). */
   x: number;
@@ -34,6 +37,23 @@ export function worldPositionOf(handle: EntityHandle): { x: number; y: number; z
   return result;
 }
 
+/** Whether a handle and every ancestor of it are switched on (see `properties/enabled.ts`). */
+export function isHandleEnabled(handle: EntityHandle): boolean {
+  return enabledAlongChain(handle, (h) => h.props, (h) => h.parent);
+}
+
+/** Where the mouse is (world units) and what it did this frame. */
+export interface PointerState {
+  x: number;
+  y: number;
+  /** Whether the pointer is over the game view at all. */
+  inside: boolean;
+  down: boolean;
+  /** Went down / up during this frame. */
+  pressed: boolean;
+  released: boolean;
+}
+
 /**
  * Services a graph may use while running. Implemented by the runtime (BehaviorSystem) and
  * by test doubles. Everything the graph does to the world goes through here, so the core
@@ -51,6 +71,14 @@ export interface NodeContext {
   dt: number;
   findByName(name: string): EntityHandle | null;
   isKeyDown(key: string): boolean;
+  /** Mouse state of this frame, in world units (see `PointerState`). */
+  pointer: PointerState;
+  /**
+   * Whether a world point lies on `target` – on its colliders when it has any, otherwise on
+   * its own footprint or that of anything parented below it (so a button made of a container
+   * with a sprite and a label is hit as a whole).
+   */
+  hitTest(target: EntityHandle, x: number, y: number): boolean;
   /**
    * Whether any collider of `a` overlaps any collider of `b` right now. A collider entity
    * stands for itself; any other entity stands for its direct collider children.
@@ -70,6 +98,8 @@ export interface NodeContext {
   spawn(assetId: string, position: { x: number; y: number; z: number }, parent: EntityHandle | null): EntityHandle | null;
   destroy(target: EntityHandle): void;
   stop(): void;
+  /** Ends the run and starts it again from the saved scene (everything spawned is lost). */
+  restart(): void;
 }
 
 export interface PortDef {