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/api/__init__.py

@@ -0,0 +1,39 @@
+"""REST API routers (SPEC §9.1). One module per route group."""
+
+from __future__ import annotations
+
+from fastapi import FastAPI
+
+
+def register_routers(app: FastAPI) -> None:
+    """Mount all API routers under the ``/api`` prefix.
+
+    Routers are added milestone by milestone; imports are local so the app
+    factory stays importable while modules are still being built out.
+    """
+    from app.api.accounts import router as accounts_router
+    from app.api.actions import router as actions_router
+    from app.api.compose import router as compose_router
+    from app.api.mailboxes import router as mailboxes_router
+    from app.api.messages import router as messages_router
+    from app.api.recipients import router as recipients_router
+    from app.api.search import router as search_router
+    from app.api.settings import router as settings_router
+    from app.api.threads import router as threads_router
+    from app.identity.routes import router as auth_router
+    from app.ws import router as ws_router
+
+    for router in (
+        auth_router,
+        accounts_router,
+        threads_router,
+        messages_router,
+        search_router,
+        actions_router,
+        compose_router,
+        recipients_router,
+        settings_router,
+        mailboxes_router,
+    ):
+        app.include_router(router, prefix="/api")
+    app.include_router(ws_router, prefix="/api")