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/redis_client.py

@@ -0,0 +1,42 @@
+"""Shared async Redis client (sessions, rate limits, pub/sub, arq)."""
+
+from __future__ import annotations
+
+from collections.abc import Awaitable
+from typing import Any, cast
+
+import redis.asyncio as aioredis
+
+from app.config import get_settings
+
+
+def aw(result: Any) -> Awaitable[Any]:
+    """Normalize a redis-py ``ResponseT`` (``Awaitable | value``) to an awaitable.
+
+    Some redis-py async commands (hash ops, getdel, ...) are typed as a
+    sync/async union; this keeps call sites awaitable under ``mypy --strict``.
+    """
+    return cast("Awaitable[Any]", result)
+
+
+_client: aioredis.Redis | None = None
+
+
+def get_redis() -> aioredis.Redis:
+    """Return (creating on first use) the process-wide Redis client."""
+    global _client
+    if _client is None:
+        _client = aioredis.Redis.from_url(
+            get_settings().redis_url,
+            encoding="utf-8",
+            decode_responses=True,
+        )
+    return _client
+
+
+async def close_redis() -> None:
+    """Close the Redis client (used on app shutdown)."""
+    global _client
+    if _client is not None:
+        await _client.aclose()
+        _client = None