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/services/message_service.py

@@ -0,0 +1,30 @@
+import uuid
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models import Message
+
+
+async def create_message(
+    db: AsyncSession, room_id: uuid.UUID, user_id: uuid.UUID, content: str
+) -> Message:
+    message = Message(room_id=room_id, user_id=user_id, content=content)
+    db.add(message)
+    await db.commit()
+    await db.refresh(message)
+    return message
+
+
+async def list_recent_messages(
+    db: AsyncSession, room_id: uuid.UUID, limit: int = 50
+) -> list[Message]:
+    result = await db.execute(
+        select(Message)
+        .where(Message.room_id == room_id)
+        .order_by(Message.created_at.desc())
+        .limit(limit)
+    )
+    messages = list(result.scalars().all())
+    messages.reverse()
+    return messages