Add new output formatting system with flags for color and emoji control:
- Introduce OutputConfig and Writer structs for flexible output handling
- Add --colors and --emoji/--no-emoji global flags
- Refactor commands to use new Writer for consistent formatting
- Separate error content from presentation for better flexibility
- Add lnk status command to show repository sync status
- Add lnk push command for smart staging, committing, and pushing
- Add lnk pull command with automatic symlink restoration
- Add comprehensive sync functionality to git and core packages
- Add 5 new integration tests for sync commands (17 total tests)
- Update README with sync workflow examples and documentation
- Support commits ahead/behind tracking relative to remote
- Implement change detection to avoid empty commits
- Add graceful error handling for missing remotes
Closes: Phase 1 sync implementation
