Fix issue #5099: [Bug]: When a github token expires, the waiting list screen appears

[openhands-agent]

This pull request fixes #5099.

The PR successfully addresses the core issue by implementing proper handling of expired GitHub tokens. The key improvements made:

1. Better user experience: Instead of showing a confusing waitlist screen, users now see a clear "GitHub Token Expired" message
2. Proper token management: The system now automatically detects and clears expired tokens
3. Streamlined reconnection: Users are provided with a direct "Reconnect to GitHub" button rather than being sent to a waitlist
4. Technical implementation: Changes to both waitlist-modal.tsx and _oh.tsx provide a complete solution for token expiration handling

These changes directly solve the reported problem of users being incorrectly shown a waitlist message when their GitHub token expires, and implements the requested solution of properly noting the token expiration and providing a way to enter a new one.

For a human reviewer: This PR implements proper GitHub token expiration handling by updating the UI to show clear expiration messages and adding the necessary token management logic. The changes improve the user experience by eliminating confusion and providing a straightforward path to reconnection when tokens expire.

Automatic fix generated by OpenHands 🙌

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:c7c3b34-nikolaik   --name openhands-app-c7c3b34   docker.all-hands.dev/all-hands-ai/openhands:c7c3b34