feat(select): add per-tile checkbox selection in Admin grid and all gallery layouts; tile click opens viewer; checkbox toggles selection; auto-enable selection mode; add testids

frontend/src/components/gallery/PhotoGridWithLayouts.tsx

@@ -81,6 +81,14 @@ export const PhotoGridWithLayouts: React.FC<PhotoGridWithLayoutsProps> = ({
   };
 
   const handlePhotoSelect = (photoId: number) => {
+    // Auto-enable selection mode when selecting via checkbox
+    if (!isSelectionMode) {
+      if (parentToggleSelectionMode) {
+        parentToggleSelectionMode();
+      } else {
+        setLocalSelectionMode(true);
+      }
+    }
     const newSelected = new Set(selectedPhotos);
     if (newSelected.has(photoId)) {
       newSelected.delete(photoId);
@@ -279,4 +287,4 @@ export const PhotoGridWithLayouts: React.FC<PhotoGridWithLayoutsProps> = ({
       )}
     </>
   );
-};
+};