docs: sync Chinese README with latest English version (34 use cases)

- Update use case count badge from 30 to 34
- Add Discord badge
- Add new use case translations:
  - 播客制作流水线 (Podcast Production Pipeline)
  - 习惯追踪与签到 (Habit Tracker & Checkins)
  - 自动会议笔记与行动项 (Meeting Notes & Action Items)
  - 习惯追踪与责任教练 (Habit Tracker & Accountability Coach)
  - 构建前想法验证器 (Pre-Build Idea Validator)
- Update last sync date to 2026-02-28