Build gallery Rune

Summary

Multi-image container with grid, carousel, or masonry layout and optional lightbox overlay. This is a core rune — it belongs in packages/runes/src/tags/, not in a community package.

Status

Already implemented. Schema, config, CSS, and edit hints all exist:

• Schema: packages/runes/src/tags/gallery.ts (uses createContentModelSchema)
• Type: packages/runes/src/schema/gallery.ts
• Config: packages/runes/src/config.ts (block gallery, modifiers for layout/lightbox/gap/columns)
• CSS: packages/lumina/styles/runes/gallery.css (grid, carousel, masonry layouts + lightbox overlay)
• Registry: Gallery → ImageGallery in packages/runes/src/registry.ts