- Fix category_name from "典藏" to "普通" for regular type
- Clarify 6 items max display (更多> not counted)
- Document cover_url_signed is generated on-the-fly, not stored
- Add star_id comes from JWT context note
- Document Gateway NULL→0 conversion for grade
- Add toChineseGrade helper function for frontend
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>