feat(core,server,web,cli): show version in the web UI with update check and admin self-update (#74)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/docs/content/configuration.en.md

@@ -18,6 +18,7 @@ The CLI and the server automatically load a `.env` file from the working directo
 | `PENGUIN_WEB_DIST` | Front-end static assets directory | the npm server package falls back to its bundled web-dist |
 | `PENGUIN_PREVIEW_ORIGIN` | Origin that serves Workspace HTML previews, e.g. `https://preview.example.com` | unset — the loopback counterpart is derived per request |
 | `PENGUIN_LANG` | CLI language (`en` / `zh`), set via `penguin config lang` | `en` |
+| `PENGUIN_UPDATE_CHECK` | `off` disables the web app's new-release check (the server's only outbound internet call) | enabled |
 
 `PENGUIN_PREVIEW_ORIGIN` must differ from the app's origin by **hostname**, not just port: cookies ignore ports, so a second port would still share the session cookie. Leave it unset for local use — the app is canonicalized onto `localhost` and previews are served from `127.0.0.1`, which needs no configuration and no DNS. Set it when the app is reached over a LAN address or a real domain; otherwise previews there fall back to a same-origin sandbox where `localStorage`, cookies and third-party embeds do not work. When you do set it on a real domain, keep the session cookie host-only (no `Domain=`), or a sibling subdomain shares it. An unparseable value is a startup error rather than a silent fallback.