Share a link that plays the game without the editor (#266)

A project could only be played inside the editor, behind the login.
To show a game to someone else there was no way short of an account.
A release freezes the saved project under a random token and serves
it on a page that holds nothing but the game view.

- Menu -> Release... opens a dialog with the state of the release,
  the link with Copy link and Open, Publish or Update release, and
  Take down behind a confirmation.
- Publish saves first and refuses while anything is unsaved, like
  snapshots. Updating keeps the link. Take down kills it, and a new
  Publish hands out a new token.
- The link is play.html?game=<32 hex>. The page needs no session,
  paints Theme.colors.background, zooms with Auto and waits for
  "Click to play" so that sound and keyboard focus are allowed.
- The game always starts in the start scene. Persistent variables
  are stored per link in the browser. Plugins are not loaded, and the
  dialog warns about them and about a project without a scene.
- GET ?r=releases/{token} is the only route besides auth/* that works
  without a login. The public answer carries the token as project.id,
  so the project id stays hidden. Release files are written with 0640
  and nginx does not serve them directly (measured 403).
- Starting, the frame and Load scene moved into runtime/GameRun.ts.
  Play in the editor and the play page run through the same code.
- WorldViewport moved to src/viewport/ and no longer needs the
  EditorState. Pointer forwarding (gamePointer.ts) and setting up
  textures, fonts and sounds (projectFiles.ts) exist only once.
- Vite builds two pages. The play page loads 4 kB of its own code
  plus the shared chunk (Pixi, runtime, drawing, 653 kB) and Rapier,
  without the editor.

Found on the way, not fixed here: data/projects/<id>.json answers 200
without a login because the files are 0644.

Tests:
- ./check.sh: 194 files, 2808 tests, exit 0.
- tests/php/releases.test.php: 20 checks, also added to CI.
- New e2e module 60 with 10 checks, played in a browser without a
  session. Module 46 counts the menu entries and was updated.
- Full e2e run: 1572 checks passed.
- Counter-checks: 3 unit, 2 PHP and 3 browser mutations all fail.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/debug/renderHooks.ts

@@ -1,24 +1,16 @@
 import { type FrameRect, isTextureFile, resolvePicture } from '../../core/model/texture';
 import { effectiveScale, gameClock } from '../../core/time';
-import { afterFrames, isRendering, renderCount, requestRender } from '../../ui';
+import { afterFrames, isRendering, renderCount, requestRender, stagePixel } from '../../ui';
 import { particleLibrary } from '../../viewport/ParticleLibrary';
 import { shaderLibrary } from '../../viewport/ShaderLibrary';
 import { textureLibrary } from '../../viewport/TextureLibrary';
-import { type Container, Mesh, Rectangle } from 'pixi.js';
+import { type Container, Mesh } from 'pixi.js';
 import type { HookContext } from './hookHelpers';
 
 /** What was really drawn, and the clocks behind it: pixels, textures, frames, shaders and particles. */
 export function renderHooks({ app, state, editor }: HookContext) {
   const { viewport, gameView } = editor;
-  /** The colour actually on screen at a point, as `#rrggbb` – what was drawn, not what the model says. */
-  const pixelAt = (x: number, y: number): string => {
-    const { pixels } = app.renderer.extract.pixels({
-      target: app.stage,
-      frame: new Rectangle(x, y, 1, 1),
-    });
-    const hex = (value: number | undefined) => (value ?? 0).toString(16).padStart(2, '0');
-    return `#${hex(pixels[0])}${hex(pixels[1])}${hex(pixels[2])}`;
-  };
+  const pixelAt = (x: number, y: number): string => stagePixel(app, x, y);
   return {
     pixelAt,
     /**