- Add ForumTopicRead, ForumReplyRead, ClassifiedRead models
- Add SQL migration for new tables
- Record reads when user views forum topic (topic + all visible replies)
- Record reads when user views B2B classified
- Display "Seen by" avatars in forum topic and B2B detail pages
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
