- Add media_items array support to ticket messages (types, API clients)
- Create shared MessageMediaGrid component with photo grid, fullscreen
viewer, keyboard nav, video/document rendering
- Replace per-page AdminMessageMedia/MessageMedia with MessageMediaGrid
- Add linkifyText util (DOMPurify-sanitized) for auto-linking URLs
- Support multi-file upload (up to 10) in AdminTickets and Support pages
- Remove unused ticketsApi import from AdminUserDetail
