feat: improve monitor info output with grouped region display (#13)
Display regions grouped by provider (Fly.io, Koyeb, Railway) with short
codes instead of raw enum values for better readability.
- Add Koyeb and Railway region mappings to regionToString()
- Fix regionsToStrings() to use regionToString() for consistent short codes
- Add groupRegionsByProvider() to categorize regions by provider
- Update monitor info display to show each provider on its own row