* feat: add avatar metrics tracking feature (#110)
Add AvatarMetrics dataclass for tracking avatar state snapshots
- Add AvatarMetrics dataclass for recording monthly snapshots
- Add metrics_history field to Avatar with opt-in tracking
- Implement automatic monthly snapshot recording in Simulator
- Add backward compatibility support for existing save files
- Set default tracking limit to 1200 months (100 years)
- Add comprehensive tests with 100% coverage
- Move documentation to specs directory with simplified chinese
* fix: convert Traditional Chinese comments to Simplified Chinese
修正程式碼中的繁體中文註解為簡體中文，以符合專案規範。
Fix Traditional Chinese comments to Simplified Chinese in codebase.
