Switch between plan mode and build mode for structured workflow.

Operations:
- enter: Request to switch to plan mode for research and planning
- exit: Request to exit plan mode and switch to build mode

**Enter Plan Mode (operation: "enter")**

Call this tool when:
- The user's request is complex and would benefit from planning first
- You want to research and design before making changes
- The task involves multiple files or significant architectural decisions
- If they explicitly mention wanting to create a plan ALWAYS call this tool first

Do NOT call this tool:
- For simple, straightforward tasks
- When the user explicitly wants immediate implementation

After entering plan mode:
- Research the requirements
- Create a detailed plan file
- Use plan_exit tool when planning is complete

**Exit Plan Mode (operation: "exit")**

Call this tool when:
- You have written a complete plan to the plan file
- You have clarified any questions with the user
- You are confident the plan is ready for implementation

Do NOT call this tool:
- Before you have created or finalized the plan
- If you still have unanswered questions about the implementation
- If the user has indicated they want to continue planning
