Fix: Auto-refresh file content when selected file changes

[tofarr]

This PR fixes the issue where the file content in the workspace panel does not automatically refresh when the selected file changes externally. Now, when a file is selected and its content changes, it will automatically update without requiring the user to click on the file again.

Changes:

• Added Redux store selector to get current agent state in TreeNode component
• Added useEffect hook to trigger file content refetch when:
  • File is currently selected
  • File is not a directory
  • Agent state changes

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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:217f8d3-nikolaik   --name openhands-app-217f8d3   docker.all-hands.dev/all-hands-ai/openhands:217f8d3

[mamoodi]

Should fix: #4968