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/migrations/env.py

@@ -0,0 +1,57 @@
+"""Alembic environment — async engine, config sourced from app settings."""
+
+from __future__ import annotations
+
+import asyncio
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy.ext.asyncio import async_engine_from_config
+from sqlalchemy.pool import NullPool
+
+# Import models so Base.metadata is populated for autogenerate.
+import app.models  # noqa: F401
+from app.config import get_settings
+from app.db import Base
+
+config = context.config
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+config.set_main_option("sqlalchemy.url", get_settings().database_url)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    context.configure(
+        url=get_settings().database_url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection: object) -> None:
+    context.configure(connection=connection, target_metadata=target_metadata)  # type: ignore[arg-type]
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_migrations_online() -> None:
+    connectable = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=NullPool,
+    )
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+    await connectable.dispose()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    asyncio.run(run_migrations_online())