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/security.py

@@ -0,0 +1,15 @@
+from argon2 import PasswordHasher
+from argon2.exceptions import VerifyMismatchError
+
+_hasher = PasswordHasher()
+
+
+def hash_password(password: str) -> str:
+    return _hasher.hash(password)
+
+
+def verify_password(password: str, password_hash: str) -> bool:
+    try:
+        return _hasher.verify(password_hash, password)
+    except VerifyMismatchError:
+        return False