changed db engine to mysql

backend/app/database.py

@@ -1,4 +1,4 @@
-"""FluentGerman.ai — Database setup (async PostgreSQL)."""
+"""FluentGerman.ai — Database setup (async MySQL)."""
 
 from collections.abc import AsyncGenerator
 
@@ -7,7 +7,11 @@ from sqlalchemy.orm import DeclarativeBase
 
 from app.config import get_settings
 
-engine = create_async_engine(get_settings().database_url, echo=get_settings().debug)
+engine = create_async_engine(
+    get_settings().database_url,
+    echo=get_settings().debug,
+    pool_recycle=3600,  # Reconnect before MySQL's wait_timeout (default 8h)
+)
 async_session = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)