Add support for `opencode run --session id /undo`

[remorses]

I would like to programmatically undo the last message of a session

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Undo tool or Undo feature #1048: Requests an undo tool/feature to revert agent changes, with similar motivation for undoing unwanted modifications
• Editing / retrying messages in the history #566: Requests editing/retrying messages in history, which includes the ability to go back and modify conversation flow
• feature: ability to rewind #338: Requests a rewind feature to roll back file changes and messages to previous points, very similar concept to undo
• feature: CLI session interaction #315: Requests CLI session interaction capabilities including message management, which overlaps with programmatic session control

Feel free to ignore if none of these address your specific case.

[remorses]

I ended up using the sdk instead for this use case