fix: fix long-term-mem utf-8 error

Author: zakahan

veadk/memory/long_term_memory.py

@@ -81,7 +81,7 @@ def _filter_and_convert_events(self, events: list[Event]) -> list[str]:
             # convert: to string-format for storage
             message = event.content.model_dump(exclude_none=True, mode="json")
 
-            final_events.append(json.dumps(message))
+            final_events.append(json.dumps(message, ensure_ascii=False))
         return final_events
 
     @override