refactor: improve write_todos tool and UI components

- Refactored the write_todos tool to enhance argument and result schemas using Zod for better validation and type safety.
- Updated the WriteTodosToolUI to streamline the rendering logic and improve loading states, ensuring a smoother user experience.
- Enhanced the Plan and TodoItem components to better handle streaming states and display progress, providing clearer feedback during task management.
- Cleaned up code formatting and structure for improved readability and maintainability.

surfsense_backend/app/agents/new_chat/tools/write_todos.py

@@ -5,7 +5,7 @@ This module provides a tool for creating and displaying a planning/todo list
 in the chat UI. It helps the agent break down complex tasks into steps.
 """
 
-from typing import Any, Literal
+from typing import Any
 
 from langchain_core.tools import tool
 
@@ -91,4 +91,3 @@ def create_write_todos_tool():
         }
 
     return write_todos
-