Serve hashed assets from R2 via CDN_BASE (#3773)

## Description:

Add an optional CDN_BASE env var that prefixes hashed asset URLs from
asset-manifest.json, so the app can serve static assets from R2/CDN
instead of the app origin. The value is determined at runtime via the
EJS template (window.CDN_BASE) — empty string means "same origin,"
matching today's behavior.

A hack to load the worker bundle:

A same-origin Blob script that dynamic-import()s the cross-origin worker
module and buffers early postMessage calls until the imported module's
handler attaches, sidestepping the browser's refusal to construct a
Worker directly from a cross-origin URL.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

docs/Architecture.md

@@ -28,3 +28,13 @@ When a user performs an action, it creates an "Intent" which is sent to the serv
 6. All executions run
 7. At the end of the tick core sends updates to client
 8. Client renders the updates
+
+## Static Assets / CDN
+
+The game server only renders `index.html` and serves the websocket. Every other asset (the Vite JS/CSS bundle, images, map binaries, the worker module) is served from a CDN bucket. Setting `CDN_BASE` to an empty string falls back to same-origin and is the dev default.
+
+### `CDN_BASE` format
+
+- Full origin, no path, no trailing slash: `https://cdn.example.com`
+- Set as a build-time variable in `vite.config.ts` (so the manifest is built with absolute URLs) and as a runtime env var on the server (so `RenderHtml.ts` can prefix Vite's emitted `/assets/...` refs at request time).
+- Configured in CI via `vars.CDN_BASE` in `.github/workflows/{deploy,release}.yml`.