fix: Update type hints to use newer Python syntax

- Replace Dict, List, Optional with dict, list,  < /dev/null |  None syntax
- Fix abstract method implementation in message.py
- Improve type annotations and function return types
- Remove unreachable code in get_current_task_tool.py
- Refactor HTML elements to use style attributes

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

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

src/plugins/PFC/chat_observer.py

@@ -23,6 +23,7 @@ class ChatObserver:
 
         Args:
             stream_id: 聊天流ID
+            private_name: 私聊名称
 
         Returns:
             ChatObserver: 观察器实例