Translation on Firefox Translations models; new logo

- Email translation moves from LibreTranslate to our own translator
  service (translator/): Mozilla's Firefox Translations models on the
  Bergamot engine, fastText language detection (176 languages). Polish,
  English, German, French, Spanish and Italian on first start (~350 MB
  instead of ~10 GB); Admin panel > Email translation installs and
  removes languages. Built and pushed as the `translator` image.
- Every message is translated paragraph by paragraph as plain text;
  names travel with their sentence and are kept only where the model
  changed them; a sentence start the model copied ("Enclosed") is tried
  again in lower case; list markers are not sent
- The Translate button shows only for installed languages
- New logo: favicon, app/maskable/iPhone icons, notification badge,
  email logo and calendar copy regenerated; BIMI logo rebuilt in SVG
  Tiny PS with its gradients; masks render in browsers
- Launch screen background is the app's dark grey

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

frontend/src/i18n/en.ts

@@ -691,6 +691,20 @@ export const en = {
   "admin.testTo": "Send a test email to",
   "admin.sendTest": "Send test",
   "admin.testSent": "Test email sent.",
+  "admin.translation": "Email translation",
+  "admin.translationHelp":
+    "Languages email can be translated between, all on this server (Mozilla's Firefox Translations models). Each language is about 70 MB: models to and from English, through which other pairs go.",
+  "admin.translationOff": "Translation is off on this server (TRANSLATOR_URL is empty).",
+  "admin.translationUnreachable": "The translation service is not answering. It may still be starting.",
+  "admin.translationAlways": "always installed",
+  "admin.translationRemove": "Remove",
+  "admin.translationRemoveTitle": "Remove {language}?",
+  "admin.translationRemoveConfirm": "Its models are deleted. Mail in this language can no longer be translated until it is installed again.",
+  "admin.translationInstalling": "downloading… {percent}%",
+  "admin.translationFailed": "Installing {language} failed:",
+  "admin.translationChoose": "Add a language…",
+  "admin.translationInstall": "Install",
+  "admin.translationCatalogueOffline": "Mozilla's list of languages can't be reached right now, so no more can be added.",
   "admin.users": "Users",
   "admin.userSearch": "Search by login, email address or name…",
   "admin.noUsers": "No users match.",