Complete training workflow and acceptance hardening

backend/app/db/base.py

@@ -20,7 +20,15 @@ _sessionmaker: async_sessionmaker[AsyncSession] | None = None
 def get_engine():
     global _engine
     if _engine is None:
-        _engine = create_async_engine(get_settings().database_url, pool_pre_ping=True)
+        settings = get_settings()
+        _engine = create_async_engine(
+            settings.database_url,
+            pool_pre_ping=True,
+            pool_size=settings.db_pool_size,
+            max_overflow=settings.db_pool_max_overflow,
+            # SQLAlchemy exceptions/logs must not echo bound user/report values.
+            hide_parameters=True,
+        )
     return _engine