The CloneDivergenceCheck was running `git fetch --quiet` without any
timeout, causing `gt doctor` to hang indefinitely when any git clone
had network issues, SSH key prompts, or credential dialogs.
Added timeouts to potentially blocking network operations:
- git fetch --quiet: 5 second timeout
- git pull --rebase: 30 second timeout
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>