fix: video upload media type, select all, and dimension repair (#203, #220, #180)

- Fix admin video upload missing media_type/mime_type and video processing (#203)
- Fix Gallery-Premium Select All using atomic callbacks instead of stale closure loop (#220)
- Add photo dimension repair endpoint and admin UI (#180)
- Add E2E tests for all three fixes

frontend/src/components/gallery/PhotoGridWithLayouts.tsx

@@ -215,6 +215,8 @@ export const PhotoGridWithLayouts: React.FC<PhotoGridWithLayoutsProps> = ({
     useCanvasRendering,
     isSelectionMode,
     onPhotoSelect: handlePhotoSelect,
+    onSelectAll: selectAll,
+    onDeselectAll: deselectAll,
     eventName,
     eventLogo,
     eventDate,

frontend/src/components/gallery/layouts/BaseGalleryLayout.tsx

@@ -13,6 +13,8 @@ export interface BaseGalleryLayoutProps {
   selectedPhotos?: Set<number>;
   isSelectionMode?: boolean;
   onPhotoSelect?: (photoId: number) => void;
+  onSelectAll?: () => void;
+  onDeselectAll?: () => void;
   eventName?: string;
   eventLogo?: string | null;
   eventDate?: string | null;

frontend/src/components/gallery/layouts/GalleryPremiumLayout.tsx

@@ -165,6 +165,8 @@ export const GalleryPremiumLayout: React.FC<GalleryPremiumLayoutProps> = ({
   selectedPhotos = new Set(),
   isSelectionMode = false,
   onPhotoSelect,
+  onSelectAll,
+  onDeselectAll,
   eventName,
   eventDate,
   allowDownloads = true,
@@ -287,17 +289,11 @@ export const GalleryPremiumLayout: React.FC<GalleryPremiumLayoutProps> = ({
 
   const handleSelectAll = useCallback(() => {
     if (selectedPhotos.size === filteredPhotos.length) {
-      // Deselect all
-      filteredPhotos.forEach(p => onPhotoSelect?.(p.id));
+      onDeselectAll?.();
     } else {
-      // Select all
-      filteredPhotos.forEach(p => {
-        if (!selectedPhotos.has(p.id)) {
-          onPhotoSelect?.(p.id);
-        }
-      });
+      onSelectAll?.();
     }
-  }, [selectedPhotos, filteredPhotos, onPhotoSelect]);
+  }, [selectedPhotos, filteredPhotos, onSelectAll, onDeselectAll]);
 
   const handleDownloadSelected = useCallback(async () => {
     if (selectedPhotos.size === 0) return;