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/schemas/auth.py

@@ -0,0 +1,6 @@
+from pydantic import BaseModel, Field
+
+
+class LoginRequest(BaseModel):
+    username_or_email: str = Field(min_length=1)
+    password: str = Field(min_length=1)