Add gallery image starring and starred images gallery

[Mundisoft]

Summary

• add a star control in Gallery mode to star/unstar the current image
• save starred items as a cross-thread list of remembered links (starredGalleryImages)
• add a top-bar “Starred” shortcut to open a gallery view of starred items
• add a per-image star control next to the file download icon in file info, so images can be starred outside Gallery mode

Notes

• starred state is synchronized across Gallery mode and file-info star controls using shared storage
• includes UI/CSS updates for star controls and starred thumbnail handling in the gallery
• current focus is URL-based starred links (not local media archiving)

[Mundisoft]

I’d appreciate feedback on the direction of this starred-images feature.

If this feature is interesting, I’m happy to also implement one or both of these additions as part of this PR:

• Add a “Clear starred images” action (header/menu)
• Add a cleanup action to remove starred entries whose source URLs are dead

Another possible direction (instead of link-based stars that can become dead) is to store starred media locally via IndexedDB. If that’s of interest, I’m happy to look into it.

Implementation note: the current starred list uses the existing storage abstraction, which may be shared between normal and private windows depending on environment. If this is a concern, I can investigate a localStorage-scoped approach for starred images instead of using the current storage abstraction.