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/workers/worker.py

@@ -14,10 +14,12 @@ from typing import Any
 
 from arq import func
 
+from app.completion import build_index_job
 from app.indexer.attachments import dedupe_existing_job
 from app.outbox.draft_sync import push_draft_to_imap_job, remove_imap_draft_job
 from app.outbox.jobs import file_sent_copy_job, send_job
 from app.push.service import push_new_mail_job
+from app.subscriptions import backfill_list_headers_job
 from app.sync.actions import (
     ACTION_MAX_TRIES,
     delete_thread_job,
@@ -67,4 +69,11 @@ BULK_FUNCTIONS = [
     sync_bootstrap_account,
     # Resumable (each batch is saved), so a long first run may span timeouts.
     func(dedupe_existing_job, timeout=6 * 3600),
+    # Batches are saved as they go, so a run cut short resumes where it stopped.
+    # No stored result: its job id (one per user) must only block a second run
+    # while one is queued or running — a kept result would refuse new scans for
+    # an hour after each one.
+    func(backfill_list_headers_job, timeout=6 * 3600, keep_result=0),
+    # Sentence completion: one per user at a time, and none kept (as above).
+    func(build_index_job, timeout=1800, keep_result=0),
 ]