Fix issue #6262: Add success/failure indicators for file read/edit operations

[neubig]

This pull request fixes #6262.

The changes made directly address the core issue and implement the requested functionality:

1. Added success/failure indicators for file read/edit operations in the chat interface
2. Added tests to verify the behavior
3. Implemented success detection based on content presence and absence of error messages

The changes are minimal and focused on the core functionality, with no unnecessary modifications to other files.

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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:2fd9e3c-nikolaik   --name openhands-app-2fd9e3c   docker.all-hands.dev/all-hands-ai/openhands:2fd9e3c

[amanape]

LGTM