Fix thumbnail loading and startup gallery refresh.

Refresh gallery metadata after thumbnail generation so new thumb URLs are available immediately, and lazy-load gallery thumbnails with IntersectionObserver to avoid fetching all images on initial page load.

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

app/internal/handlers/handlers.go

@@ -70,6 +70,17 @@ func New(imagesDir, staticDir string, mailCfg *mail.Config) (*Server, error) {
 	} else {
 		log.Print("gallery thumbnails: ready")
 	}
+	// Thumbnail URLs are resolved during gallery.List. Re-list after derivative
+	// generation so newly-created thumbs appear immediately on first load.
+	if refreshed, err := gallery.List(imagesDir); err != nil {
+		log.Printf("gallery refresh after thumbnails: %v", err)
+	} else {
+		srv.Images = refreshed
+		if hero, hasHero := gallery.SelectHero(refreshed); hasHero {
+			srv.Hero = hero
+			srv.HasHero = true
+		}
+	}
 	return srv, nil
 }