feat: add automatic PR generation

[MusicMaster4]

Summary

• Adds gg status for compact branch and file status
• Introduces gg log [n] for pretty recent commit history
• Enables gg undo to un-commit the last change and stage it
• Adds gg amend [-m] to stage all and amend the last commit
• Includes gg stash [pop|list] for parking and restoring work
• Improves gg restore to discard staged changes too
• Automates pushing to upstream when creating a PR
• Enhances gg doctor with parallel checks
• Updates gg help with grouped commands

Test plan

• Verify gg status displays correct branch and file status
• Confirm gg log [n] shows the expected commit history
• Test gg undo by staging changes, undoing, and verifying the commit is removed
• Ensure gg amend correctly stages all and amends the last commit
• Check gg stash saves and restores work-in-progress correctly
• Validate gg restore discards staged changes
• Confirm PR creation with gg pr includes the correct title and description
• Run gg doctor and verify all checks pass in parallel

[greptile-apps]

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