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/snooze.py

@@ -0,0 +1,76 @@
+"""Snooze endpoints: hide a conversation from the Inbox until a set time."""
+
+from __future__ import annotations
+
+import datetime as dt
+import uuid
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app import snooze
+from app.api.errors import raise_api_error
+from app.db import get_session
+from app.events import get_event_bus
+from app.identity.deps import CurrentUser, require_csrf
+from app.models import Thread
+
+router = APIRouter(prefix="/threads", tags=["mail"], dependencies=[Depends(require_csrf)])
+
+DbSession = Annotated[AsyncSession, Depends(get_session)]
+
+
+class SnoozeIn(BaseModel):
+    until: dt.datetime
+
+
+class SnoozeOut(BaseModel):
+    thread_id: uuid.UUID
+    snoozed_until: dt.datetime | None
+
+
+async def _thread(db: AsyncSession, user_id: uuid.UUID, thread_id: uuid.UUID) -> Thread:
+    thread = await db.scalar(
+        select(Thread).where(Thread.id == thread_id, Thread.user_id == user_id)
+    )
+    if thread is None:
+        raise_api_error(404, "not_found", "thread not found")
+    return thread
+
+
+async def _announce(user_id: uuid.UUID, thread_id: uuid.UUID) -> None:
+    await get_event_bus().publish(
+        "thread.updated", {"user_id": str(user_id), "thread_id": str(thread_id)}
+    )
+
+
+@router.post("/{thread_id}/snooze", response_model=SnoozeOut)
+async def snooze_thread(
+    thread_id: uuid.UUID, body: SnoozeIn, user: CurrentUser, db: DbSession
+) -> SnoozeOut:
+    until = body.until
+    if until.tzinfo is None:
+        raise_api_error(400, "invalid_time", "the time needs a time zone")
+    now = dt.datetime.now(dt.UTC)
+    if until <= now:
+        raise_api_error(400, "invalid_time", "pick a time in the future")
+    if until > now + snooze.MAX_SNOOZE:
+        raise_api_error(400, "invalid_time", "snooze for at most a year")
+    thread = await _thread(db, user.id, thread_id)
+    snooze.snooze(thread, until, now)
+    await db.commit()
+    await _announce(user.id, thread_id)
+    return SnoozeOut(thread_id=thread_id, snoozed_until=thread.snoozed_until)
+
+
+@router.post("/{thread_id}/unsnooze", response_model=SnoozeOut)
+async def unsnooze_thread(thread_id: uuid.UUID, user: CurrentUser, db: DbSession) -> SnoozeOut:
+    thread = await _thread(db, user.id, thread_id)
+    if thread.snoozed_until is not None:
+        snooze.wake(thread, dt.datetime.now(dt.UTC))
+        await db.commit()
+        await _announce(user.id, thread_id)
+    return SnoozeOut(thread_id=thread_id, snoozed_until=None)