Fix: pymysql import crash in Docker environment

Docker installs mysqlclient natively, so pymysql isn't needed.
Use try/except to handle both environments gracefully.

backend/config/__init__.py

@@ -1,2 +1,5 @@
+try:
     import pymysql
     pymysql.install_as_MySQLdb()
+except ImportError:
+    pass  # Docker uses mysqlclient natively