fix: Ensure explicit returns and correct async calls

Adds explicit `return None` statements in several functions across different modules to improve code clarity and prevent potential issues where functions might implicitly return None.
Corrects an async call in `Heartflow.deactivate_chat` by adding `await`.
Updates type hints in `heartflow_prompt_builder.py`.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

import_openie.py

@@ -156,6 +156,7 @@ def main():
     if handle_import_openie(openie_data, embed_manager, kg_manager) is False:
         logger.error("处理OpenIE数据时发生错误")
         return False
+    return None
 
 
 if __name__ == "__main__":