docs: reflect the config, branding, i18n and plugin-API changes

- config.md: add server.guestIdent, report.service, defaults.lang; correct the
  turnstile.enabled / features.* descriptions; add a Languages section; complete example.
- branding.md: branding.name/icon now drive the favicon, notifications, PWA and push;
  fix the feature-flag notes; add a Languages note.
- plugins.md: document orbit.config() and orbit.i18n (language/t/pick) + a Localization
  section; note they arrived in apiVersion 4.
- overview.md: add the 10-language support bullet.

docs/branding.md

@@ -21,8 +21,10 @@ Everything that ties Orbit to a particular network or brand lives in
 }
 ```
 
-This changes the connect screen, the console title, the network icon, and the CTCP VERSION/SOURCE
-replies the client sends.
+`branding.name` and `branding.icon` reach **everywhere** the app identifies itself: the connect
+screen, the browser tab title + **favicon**, desktop and Web Push notifications, the PWA install
+prompt (name + description, localized), the iOS home-screen title, the network icon, and the CTCP
+VERSION/SOURCE replies. Point `icon` at your own logo URL and the tab icon follows.
 
 ## Themes
 
@@ -49,6 +51,11 @@ Hide whole features per deployment:
 { "features": { "push": true, "imageUpload": true, "register": false } }
 ```
 
-- `push` — the Web Push notifications row.
-- `imageUpload` — the composer image button + paste/drag upload.
-- `register` — the "create an account" tab.
+- `push` — Web Push notifications: the Settings row **and** the re-subscribe-on-connect.
+- `imageUpload` — the composer image button **and** paste / drag-drop upload.
+- `register` — account self-service: the "Create account" button, the "Forgot password" link, and their FAQ entries (all hidden together).
+
+## Languages
+
+The UI and the bundled plugins are fully translated in **10 languages** (auto-detected). Pin a
+default with [`defaults.lang`](https://orbit.tchatou.fr/docs/config/); users can switch in Settings.