fix(startup): remove redundant traceback import causing UnboundLocalError

Remove redundant 'import traceback' statement inside exception handler
in docker/start-fixed.py. The traceback module is already imported at
the top of the file, and the local import was causing Python to treat
it as a local variable, leading to UnboundLocalError when the exception
handler didn't execute.

docker/start-fixed.py

@@ -348,7 +348,6 @@ def run_migrations():
                     
             except Exception as e:
                 log(f"Post-migration verification failed: {e}", "ERROR")
-                import traceback
                 traceback.print_exc()
                 return None