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>

README.md

@@ -16,8 +16,17 @@ Live: <https://nockal.com/game-maker/> · Widget playground: <https://nockal.com
 | **Edit mode** | The viewport draws the project model; panels, grid, gizmos and drag-to-move are active. |
 | **Play mode** | A `World` is instantiated from the active scene (one entity per scene object, resolved properties as mutable state). Systems tick it; nothing writes back. **Stop discards the world.** |
 
-Phase-1 demo behaviour in Play: the arrow keys move the sprite that was selected when Play was
-pressed (or the first sprite); the first camera in the scene follows it.
+**The camera defines what is rendered.** A camera asset has a view size (`width` × `height`,
+default 640×360) and a `zoom`; the frame it covers in world units is `size / zoom`. In edit
+mode that frame is drawn as an outline. In play mode only that frame is rendered – fitted into
+the viewport with black letterboxing – and objects outside it are culled. A scene without a
+camera renders nothing in play mode. Play has no built-in behaviour (no input, no movement):
+behaviour will come with scripting in a later phase.
+
+**Editor symbols are always on top.** The viewport draws scene content (sprites) in an
+`objects` layer and editor symbols (camera icon, labels) in an `overlay` layer above it, so a
+sprite can never hide a symbol regardless of hierarchy order. Z-order between sprites is not
+configurable yet.
 
 ## Stack
 
@@ -34,12 +43,12 @@ pressed (or the first sprite); the first camera in the scene follows it.
 ```
 web/index.html      Vite source page (dev)            index.html   built page (generated, served)
 src/core/           model, property schema, resolve, commands, store – no Pixi imports
-src/runtime/        World, Entity, systems (Input, PlayerControl, CameraFollow)
+src/runtime/        World, Entity, System interface, Input tracker (no systems yet)
 src/ui/             widget toolkit (generic, knows nothing about assets)
 src/viewport/       scene renderer: model in edit mode, world in play mode
 src/editor/         App composition, state, panels, inspector field factory
 api/                PHP backend            data/projects/   persisted projects
-tests/              Vitest unit tests      tools/e2e.mjs    headless CDP smoke test
+tests/              Vitest unit tests      tools/           e2e.mjs (CDP smoke test), seed-demo.mjs
 ```
 
 Rules that keep it organised: `core/` imports nothing from other layers; `ui/` never sees
@@ -57,7 +66,8 @@ npm run dev          # http://localhost:5175/game-maker/dist/ – API calls are
 npm test             # unit tests (core)
 npm run typecheck
 npm run build        # writes dist/ and regenerates index.html
-node tools/e2e.mjs <projectId>   # headless end-to-end run with screenshots in /tmp/gm-e2e-*.png
+node tools/seed-demo.mjs <projectId>   # reset the demo project to the state the e2e run expects
+node tools/e2e.mjs <projectId>         # headless end-to-end run with screenshots in /tmp/gm-e2e-*.png
 ```
 
 The workspace folder itself is what nginx serves, so `npm run build` is the deployment.