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/settings.py

@@ -27,6 +27,7 @@ _ALLOWED_INVITE_FROM = {"contacts", "anyone"}
 
 # "auto", or a LanguageTool language code such as "pl-PL", "en-GB", "de".
 _LANG_CODE = re.compile(r"auto|[a-z]{2,3}(-[A-Za-z0-9]{2,8})*")
+_UI_LANGUAGE = re.compile(r"[a-z]{2,3}(-[A-Za-z]{2,4})?")
 
 
 class ReminderPref(BaseModel):
@@ -52,6 +53,16 @@ class SettingsOut(BaseModel):
     # ("auto" detects it per message).
     spellcheck_enabled: bool = True
     spellcheck_language: str = "auto"
+    # Gmail-style keyboard shortcuts in the mail view (Settings → Keyboard shortcuts).
+    shortcuts_enabled: bool = True
+    # Remove tracking pixels from mail (Settings → Privacy).
+    block_trackers: bool = True
+    # Grey sentence endings in the compose window, taken with Tab.
+    completion_enabled: bool = True
+    # Interface language ("en", "pl", …); "" until chosen — the web app then
+    # picks one from the browser on first sign-in and saves it here.
+    ui_language: str = ""
+    # Names and words email translation leaves as they are.
 
 
 class SettingsPatch(BaseModel):
@@ -68,6 +79,10 @@ class SettingsPatch(BaseModel):
     invitation_file: bool | None = None
     spellcheck_enabled: bool | None = None
     spellcheck_language: str | None = None
+    shortcuts_enabled: bool | None = None
+    block_trackers: bool | None = None
+    completion_enabled: bool | None = None
+    ui_language: str | None = None
 
 
 class QuotaOut(BaseModel):
@@ -82,6 +97,11 @@ def allowed_image_senders(user: User) -> set[str]:
     return set()
 
 
+def blocks_trackers(user: User) -> bool:
+    """Whether tracking pixels are taken out of this user's mail (on unless switched off)."""
+    return bool(user.settings.get("block_trackers", True))
+
+
 def add_allowed_image_sender(user: User, email: str) -> None:
     current = sorted(allowed_image_senders(user))
     if email.lower() not in current:
@@ -127,6 +147,10 @@ def _settings_out(user: User) -> SettingsOut:
         allowed_image_senders=sorted(allowed_image_senders(user)),
         spellcheck_enabled=bool(s.get("spellcheck_enabled", True)),
         spellcheck_language=str(s.get("spellcheck_language", "auto")),
+        shortcuts_enabled=bool(s.get("shortcuts_enabled", True)),
+        block_trackers=blocks_trackers(user),
+        completion_enabled=bool(s.get("completion_enabled", True)),
+        ui_language=str(s.get("ui_language", "")),
     )
 
 
@@ -175,6 +199,14 @@ async def patch_settings(body: SettingsPatch, user: CurrentUser, db: DbSession)
         updates["spellcheck_enabled"] = body.spellcheck_enabled
     if body.spellcheck_language is not None and _LANG_CODE.fullmatch(body.spellcheck_language):
         updates["spellcheck_language"] = body.spellcheck_language
+    if body.shortcuts_enabled is not None:
+        updates["shortcuts_enabled"] = body.shortcuts_enabled
+    if body.block_trackers is not None:
+        updates["block_trackers"] = body.block_trackers
+    if body.completion_enabled is not None:
+        updates["completion_enabled"] = body.completion_enabled
+    if body.ui_language is not None and _UI_LANGUAGE.fullmatch(body.ui_language):
+        updates["ui_language"] = body.ui_language
     user.settings = updates
     await db.commit()
     return _settings_out(user)