Productivity features, UI translations, local email translation

- Snooze (with a Snoozed folder), keyboard shortcuts with a Settings
  section, mail templates (Compose > More > Templates), a Subscriptions
  folder with bulk unsubscribe/delete, and tracker blocking with a
  Privacy toggle (on by default)
- Own dialogs instead of browser popups; emoji picker in compose; compose
  windows survive a visit to Settings
- Sentence completion learned from the user's sent mail (no AI)
- Interface in English and Polish (one file per language, English as the
  fallback), picked from the browser on first run, then kept
- Email translation on the server via LibreTranslate: Translate button
  and "Translate to...", messages in several languages translated part
  by part, names/addresses/emoji/file names/phone numbers kept, an
  animated line while translating
- Antispam "Mark as spam" loads with the message, not when the menu opens

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

backend/app/api/__init__.py

@@ -15,6 +15,7 @@ def register_routers(app: FastAPI) -> None:
     from app.api.actions import router as actions_router
     from app.api.admin import router as admin_router
     from app.api.avatar import router as avatar_router
+    from app.api.completion import router as completion_router
     from app.api.compose import router as compose_router
     from app.api.invitations import router as invitations_router
     from app.api.mailboxes import router as mailboxes_router
@@ -25,8 +26,12 @@ def register_routers(app: FastAPI) -> None:
     from app.api.saved_searches import router as saved_searches_router
     from app.api.search import router as search_router
     from app.api.settings import router as settings_router
+    from app.api.snooze import router as snooze_router
     from app.api.spellcheck import router as spellcheck_router
+    from app.api.subscriptions import router as subscriptions_router
+    from app.api.templates import router as templates_router
     from app.api.threads import router as threads_router
+    from app.api.translation import router as translation_router
     from app.identity.routes import router as auth_router
     from app.ws import router as ws_router
 
@@ -48,6 +53,11 @@ def register_routers(app: FastAPI) -> None:
         spellcheck_router,
         push_router,
         invitations_router,
+        templates_router,
+        snooze_router,
+        subscriptions_router,
+        completion_router,
+        translation_router,
     ):
         app.include_router(router, prefix="/api")
     app.include_router(ws_router, prefix="/api")