CHANGES
- Integrate notification sending into chat processing workflow
- Add --notification and --notification-command CLI flags and help
- Provide cross-platform providers: macOS, Linux, Windows with fallbacks
- Escape shell metacharacters to prevent injection vulnerabilities
- Truncate Unicode output safely for notification message previews
- Update bash, zsh, fish completions with new notification options
- Add docs and YAML examples for configuration and customization
- Add unit tests for providers and notification integration paths
