feat: revert changes made by developer agent

[AdityaHegde]

Adds a new block at the end of tool calls just before a text response from LLM.

Adds a revert button that creates a new commit reverting the changes to just before the message chain starts.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!

[ericokuma]

• @Di7design for final design for reverts/undos