Improve gallery video UX and add upload-to-publish media workflow.

Stage raw files in upload/, publish with make sync-media/publish, and polish the lightbox: autoplay, remembered volume, Escape to close, and image/video icons without poster or caption clutter.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/internal/gallery/gallery.go

@@ -16,7 +16,7 @@ type Image struct {
 	Collection     string // event subfolder label, e.g. Anniversary
 	CollectionKey  string // slug for filters
 	Filename       string // basename
-	URL            string
+	URL            string // served file URL (/images/…)
 	ThumbURL       string
 	HeroURL        string
 	IsVideo        bool