Phase 1: auth, room CRUD, WebSocket chat, PWA frontend

Invite-only FastAPI + SQLAlchemy(async) + Postgres backend (session-cookie
auth via CLI-provisioned accounts, open-room CRUD, single-instance /ws/chat)
and a React + Vite PWA frontend (login, room list, chat view). Backend tests
pass against a local Postgres DB. See README.md and backend/README.md for
setup, and ARCHITECTURE.md for the full phased design.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/dependencies.py

@@ -0,0 +1,37 @@
+import uuid
+
+from fastapi import Depends, HTTPException, Request
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.database import get_db
+from app.models import RoomMembership, User
+
+
+async def get_current_user(
+    request: Request, db: AsyncSession = Depends(get_db)
+) -> User:
+    user_id = request.session.get("user_id")
+    if not user_id:
+        raise HTTPException(status_code=401, detail="Not authenticated")
+
+    user = await db.get(User, uuid.UUID(user_id))
+    if user is None:
+        request.session.clear()
+        raise HTTPException(status_code=401, detail="Not authenticated")
+
+    return user
+
+
+async def require_room_member(
+    room_id: uuid.UUID, user: User, db: AsyncSession
+) -> RoomMembership:
+    result = await db.execute(
+        select(RoomMembership).where(
+            RoomMembership.room_id == room_id, RoomMembership.user_id == user.id
+        )
+    )
+    membership = result.scalar_one_or_none()
+    if membership is None:
+        raise HTTPException(status_code=403, detail="Not a member of this room")
+    return membership