refactor(src/services): simplify TodoService and remove unused ConfigService stop function

Remove redundant import duplication, replace uuid with os.urandom, rename completion_rate to active, update property decorator, and clean up callback handling. Also removed unused stop_config_service function.

src/services/config.py

@@ -198,13 +198,6 @@ def start_config_service() -> ConfigService:
     return _service
 
 
-def stop_config_service() -> None:
-    global _service
-    if _service is not None:
-        _service.stop()
-        _service = None
-
-
 # Convenience helpers for concise usage
 def config() -> ConfigService:
     """Get the singleton service (concise alias)."""