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/models/message.py

@@ -0,0 +1,23 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Text, func
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.models.base import Base
+
+
+class Message(Base):
+    __tablename__ = "messages"
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
+    room_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("rooms.id"), index=True, nullable=False)
+    user_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), nullable=False)
+    content: Mapped[str] = mapped_column(Text, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), index=True, nullable=False
+    )
+    edited_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
+
+    user = relationship("User")