Fix seller card counters to use proper user-facing logic.

Member since block: - use profile created_at - do not show "0 days on Xelin" - show: - "New on Xelin" for very new users - "2 weeks on Xelin" - "3 months on Xelin" - "1 year on Xelin" 4. Keep existing seller card layout 5. Do not move buttons 6. Do not change seller name/avatar/location logic Implementation: - use created_at as source for membership duration - use rating_average and reviews_count from profile or profile stats source - keep logic readable and safe for null values