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>

frontend/src/index.css

@@ -0,0 +1,20 @@
+:root {
+  font-family: system-ui, sans-serif;
+  color-scheme: light dark;
+}
+
+body {
+  margin: 0;
+}
+
+input,
+button {
+  font: inherit;
+  padding: 0.4rem;
+}
+
+label {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}