Initial commit: webmail client (M0/M1)

Three-pane webmail client.
- Backend: FastAPI + async SQLAlchemy + arq worker (Postgres/Redis), IMAP/SMTP
  sync, threading, search, drafts/outbox with undo, attachments, 2FA.
- Frontend: React 18 + Vite + TypeScript + TanStack Query + Tailwind; three-pane
  UI with rich-text composer, light/dark themes, resizable panels.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/queue.py

@@ -0,0 +1,31 @@
+"""arq queue helpers (enqueue side, used by the API)."""
+
+from __future__ import annotations
+
+from arq import create_pool
+from arq.connections import ArqRedis, RedisSettings
+
+from app.config import get_settings
+
+_pool: ArqRedis | None = None
+
+
+def redis_settings() -> RedisSettings:
+    """Return arq RedisSettings derived from ``REDIS_URL``."""
+    return RedisSettings.from_dsn(get_settings().redis_url)
+
+
+async def get_arq_pool() -> ArqRedis:
+    """Return (creating on first use) the shared arq enqueue pool."""
+    global _pool
+    if _pool is None:
+        _pool = await create_pool(redis_settings())
+    return _pool
+
+
+async def close_arq_pool() -> None:
+    """Close the arq pool."""
+    global _pool
+    if _pool is not None:
+        await _pool.aclose()
+        _pool = None