Fix hanging agent loops

[rbren]

End-user friendly description of the problem this fixes or functionality that this introduces

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Give a summary of what the PR does, explaining any non-trivial design decisions

If you create a new conversation, but the webhook never attaches, the agent loop gets orphaned and never gets cleaned up.

With this change, we call cleanup when the loop gets created, so that if no one connects after 15s it gets abandoned

Working on something more robust here as well

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Link of any specific issues this addresses

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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:993b158-nikolaik   --name openhands-app-993b158   docker.all-hands.dev/all-hands-ai/openhands:993b158