Add persistence layer: TOTP auth, game history, restore

- db/ package: async SQLAlchemy engine + Player/Game/Guess models
- api/auth.py: passwordless TOTP login (pyotp), session token via socket auth
- api/history.py: record guesses/points, DB-backed standings, restore
  unfinished games on startup, host-only end_game
- api/__init__.py: auth-gated handlers, accounts map, rejoin via account
- frontend: Auth (QR + code) and History pages, resume/end-game in lobby/table
- docker-compose: real PostgreSQL service wired via DATABASE_URL
- tests_history.py for the persistence/auth layer; refresh CLAUDE.md

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/vite.config.ts

@@ -27,7 +27,9 @@ export default defineConfig({
     host: true,
     proxy: {
       '/socket.io': {
-        target: 'http://backend:5000',
+        // Local dev defaults to localhost; docker-compose sets VITE_BACKEND_URL
+        // to the backend service (http://backend:5000).
+        target: process.env.VITE_BACKEND_URL ?? 'http://localhost:5000',
         ws: true,
         changeOrigin: true,
       },