Create a new checkpoint snapshot of the current workspace state.

Checkpoints are snapshots that can be used to restore the workspace to a previous state. This is useful as a safety net before making changes, or to mark important milestones in your work.

Parameters:
- name: Optional name for the checkpoint (e.g., "before refactoring")
- description: Optional description of the checkpoint state

The checkpoint stores all file changes and can be restored later using checkpoint_restore or undo commands.
