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>

db/db.py

@@ -0,0 +1,35 @@
+"""Async SQLAlchemy pripojenie a inicializacia schemy.
+
+Connection string z env DATABASE_URL. Default je lokalny SQLite subor (dev);
+v produkcii staci nastavit DATABASE_URL na PostgreSQL (asyncpg), kod sa nemeni.
+"""
+
+import os
+
+from sqlalchemy.ext.asyncio import (
+    AsyncSession,
+    async_sessionmaker,
+    create_async_engine,
+)
+from sqlalchemy.orm import DeclarativeBase
+
+DATABASE_URL = os.environ.get("DATABASE_URL", "sqlite+aiosqlite:///bridzik.db")
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+engine = create_async_engine(DATABASE_URL, echo=False)
+async_session: async_sessionmaker[AsyncSession] = async_sessionmaker(
+    engine, expire_on_commit=False
+)
+
+
+async def init_db() -> None:
+    """Vytvori tabulky, ak este neexistuju. Vola sa pri starte servera."""
+    # Import modelov registruje tabulky na Base.metadata.
+    from db import models  # noqa: F401
+
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)