feat(query-block): add latest activity sort option

[horacioh]

Summary

• Add "Latest activity" sort option to query blocks that orders items by the most recent comment or content change
• Update HMQuerySort schema to include the new ActivityTime sort term
• Implement activity time sorting that considers both latestChangeTime and latestCommentTime, with fallback to updateTime
• Add comprehensive test coverage for ActivityTime sorting behavior including comment priority, reversed sorting, and time fallbacks