feat: Skip export if already up-to-date

- ✨ Automatically detects if export is already current
- 🔍 Compares source festival-XX directories with exported XX directories
- ⏭️ Skips re-export when structure matches (saves time)
- 🔄 Re-exports automatically when directories don't match
- 💪 Added --force flag to override skip detection
- 📊 Shows skip status in CLI and standalone mode

This significantly speeds up repeated deployments when source hasn't changed.