Camera view frame, viewport clipping, overlay layer for editor symbols

- Camera assets get width/height properties; play mode renders only the
  camera frame (letterboxed, masked, culled) and nothing without a camera
- Remove demo arrow-key/camera-follow systems from play mode
- Clip world and gizmos to the viewport (selection frame no longer leaks
  over the left panel)
- Blur focused widget on pointerdown outside it so inspector edits commit
  before selection changes
- Separate objects/overlay layers so camera symbols always render on top
- Add tools/seed-demo.mjs for reproducible E2E runs

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

src/editor/App.ts

@@ -4,8 +4,6 @@ import { RemoveSceneObjectCommand } from '../core/commands/sceneObjectCommands';
 import { listScenes } from '../core/model/Project';
 import { HttpProjectStore } from '../core/store/HttpProjectStore';
 import type { ProjectStore } from '../core/store/ProjectStore';
-import { CameraFollowSystem } from '../runtime/systems/CameraFollowSystem';
-import { PlayerControlSystem } from '../runtime/systems/PlayerControlSystem';
 import { World } from '../runtime/World';
 import { Dialog, HStack, Menu, type MenuItem, Splitter, ui, VStack, type Widget } from '../ui';
 import { Viewport } from '../viewport/Viewport';
@@ -52,7 +50,7 @@ function installDebugHook(app: Application, state: EditorState, viewport: Viewpo
     const p = node.getGlobalPosition();
     return { x: p.x + node.width / 2, y: p.y + node.height / 2 };
   };
-  (window as unknown as { __gm: unknown }).__gm = { state, locate, viewportCenter };
+  (window as unknown as { __gm: unknown }).__gm = { state, locate, viewportCenter, viewportInfo: () => viewport.debugInfo(), layerOf: (id: string) => viewport.layerOf(id) };
 }
 
 class Editor {
@@ -187,14 +185,11 @@ class Editor {
     const scene = this.state.activeScene;
     if (!scene) return;
     ui().focus.blur();
-    const selected = this.state.selection?.kind === 'object' ? this.state.selection.objectId : null;
-    const control = new PlayerControlSystem(selected);
-    this.world = World.instantiate(this.state.project, scene.id)
-      .addSystem(control)
-      .addSystem(new CameraFollowSystem(() => control.controlled));
+    // No systems yet: the world is static. Behaviour arrives with scripting in a later phase.
+    this.world = World.instantiate(this.state.project, scene.id);
     this.viewport.setWorld(this.world);
     this.state.setMode('play');
-    this.state.setNotice('Arrow keys move the sprite · Esc stops');
+    this.state.setNotice(this.world.firstOfType('camera') ? 'Playing · Esc stops' : 'This scene has no camera – nothing is rendered · Esc stops');
   }
 
   private stop(): void {