Restore the workspace to a specified checkpoint state.

This will revert all files to their state at the time of the checkpoint. Use with caution as it will overwrite current changes.

Parameters:
- checkpoint_id: Required. The checkpoint ID or commit hash to restore to
- files: Optional. Comma-separated list of specific files to restore (partial restore)
- dry_run: Optional. If true, shows what would be restored without actually doing it

Examples:
- Full restore: checkpoint_restore checkpoint_id="abc123"
- Partial restore: checkpoint_restore checkpoint_id="abc123" files="src/index.ts,src/utils.ts"
- Preview: checkpoint_restore checkpoint_id="abc123" dry_run=true

After restore, the previous state is saved and can be restored if needed.
