Served with isolation headers; start-screen capability notices; tests on the real GPU (t88 phase 1)

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

README.md

@@ -15,8 +15,28 @@ python3 build.py
 python3 tools/serve.py            # builds, serves at http://localhost:8000 and rebuilds when src/ changes
 ```
 
-Opening `dist/index.html` directly works too. The game is one self-contained page with no
-downloads; sound and graphics are all generated in code. Saves stay in your browser.
+The game must be served: use `python3 tools/serve.py` locally, or serve `dist/` with any web
+server that sends these headers. Opening `dist/index.html` from disk is no longer supported.
+Use HTTPS when hosting remotely (localhost works over HTTP).
+
+nginx, in the site's `server` or `location` block:
+
+```nginx
+add_header Cross-Origin-Opener-Policy same-origin always;
+add_header Cross-Origin-Embedder-Policy require-corp always;
+```
+
+Caddy, in the site block alongside `root * /path/to/dist` and `file_server`:
+
+```caddyfile
+header {
+    Cross-Origin-Opener-Policy same-origin
+    Cross-Origin-Embedder-Policy require-corp
+}
+```
+
+These are plain static files, so a small server is enough. The game is one self-contained page
+with no downloads; sound and graphics are generated in code. Saves stay in your browser.
 - To keep or move a world, use Pause → Export world file.
 - To load one, use Settings → Load a world file on the title screen, or Pause → Import world file
   during a game. World files exported from the claude.ai version load here too.
@@ -36,11 +56,11 @@ You need Node (tested with 22), Python 3, and Playwright for the browser tests a
 ```sh
 uv venv .venv
 uv pip install --python .venv/bin/python -r requirements.txt
-.venv/bin/python -m playwright install chromium
+.venv/bin/python -m playwright install chromium firefox
 ```
 
 If uv is not installed, `python3 -m venv .venv` and
-`.venv/bin/pip install -r requirements.txt` also work; then install Chromium as above.
+`.venv/bin/pip install -r requirements.txt` also work; then install the browsers as above.
 After that, plain `python3` works for every command below; the browser scripts switch to
 `.venv` on their own.