Initial release: Determine if today or a given date is a working day in mainland China, using official holiday and makeup workday data.

- Queries yearly holiday-cn JSON from jsDelivr for up-to-date holiday/workday rules.
- Supports plain, date-specific, and JSON outputs for machine-readable workflows.
- Provides clear reasoning: uses official overrides when available; otherwise, falls back to weekday logic.
- Designed for both casual questions and integration into automated workflows.