Cleaner product images & a smarter thumbnail

Managing product images just got simpler.

Improvements

• Pick the thumbnail from your gallery — Every image row now has a "Use as thumbnail" option, with a badge and highlight showing the current choice. No more separate thumbnail uploader to keep in sync.
• First image is the default — If you don't pick one, the first image is automatically your thumbnail, so products are never left without one.
• No lost thumbnails — Existing products keep their thumbnail (it becomes the first gallery image), and it's never duplicated when syncing to a channel.