Upgrade the OpenHands agent monitor to reflect the new OpenHands agent format

[neubig]

The format of comments posted by the OpenHands agent has changed recently.

First, it can be triggered in two ways:

1. Sending a message to the "openhands" user: Add TestGenEval benchmark OpenHands#5534 (comment)
2. Sending adding the "openhands" tag: [Bug]: Frontend displays incorrect status message when runtime resume fails OpenHands#7225

The messages posted by the OpenHands agent are also different. We should modify the app to support this new format.

[openhands-ai]

Openhands is working, @neubig can track my progress at all-hands.dev

[neubig]

I have updated the OpenHands agent monitor to support the new format. The changes include:

• Added support for openhands-ai[bot] user
• Added support for new start work message format ("Openhands is working")
• Added support for new success message format ("can click here to [continue refining the PR]")
• Added tests for new formats

Please review PR #51