feat: Add beginner-friendly withDefaultConfig() and Easy Entry Point

- Add withDefaultConfig() for one-line setup
- Add Easy Entry Point (hua-i18n-sdk/easy) for beginners
- Add autoLanguageSync feature for automatic language change detection
- Enhance documentation with beginner-friendly guides
- Fix GitHub links and improve documentation structure
- Add comprehensive tests for withDefaultConfig()
- Update package version to 1.2.0

Breaking Changes: None
Migration: Existing code works without changes

Release: v1.1.0 – Type safety, error handling, and fallback improvements

docs: rename API Reference to SDK Reference and update all links

- Renamed API_REFERENCE.md to SDK_REFERENCE.md
- Updated all documentation links and titles to use "SDK Reference"
- Ensured consistency across README, changelog, and demo

fix: add permissions to release workflow