feat: show original filename in admin UI (#184)

Surface the existing original_filename from the database in the admin
photo grid hover overlay and photo viewer sidebar, so photographers can
correlate uploaded images with their Lightroom/disk originals. Only shown
when it differs from the system-generated filename. Gallery guests remain
unaffected.

backend/src/routes/adminPhotos.js

@@ -792,6 +792,7 @@ router.get('/:eventId/photos', adminAuth, requirePermission('photos.view'), asyn
       photos: photos.map(photo => ({
         id: photo.id,
         filename: photo.filename,
+        original_filename: photo.original_filename || null,
         // Use the correct admin photos router base for serving images
         url: `/admin/photos/${eventId}/photo/${photo.id}`,
         // Always expose a thumbnail URL; backend will generate on demand if missing

frontend/src/components/admin/AdminPhotoGrid.tsx

@@ -287,6 +287,11 @@ export const AdminPhotoGrid: React.FC<AdminPhotoGridProps> = ({
                 <p className="text-white text-xs font-medium truncate mb-1">
                   {photo.filename}
                 </p>
+                {photo.original_filename && photo.original_filename !== photo.filename && (
+                  <p className="text-white/60 text-[10px] truncate mb-1">
+                    Original: {photo.original_filename}
+                  </p>
+                )}
                 <p className="text-white/80 text-xs mb-2">
                   {photosService.formatBytes(photo.size)}
                 </p>

frontend/src/components/admin/AdminPhotoViewer.tsx

@@ -230,7 +230,11 @@ export const AdminPhotoViewer: React.FC<AdminPhotoViewerProps> = ({
 
         {/* Sidebar */}
         <div className="lg:w-80 bg-neutral-900 rounded-lg p-6 overflow-y-auto">
-          <h3 className="text-white font-medium text-lg mb-4">{currentPhoto.filename}</h3>
+          <h3 className="text-white font-medium text-lg">{currentPhoto.filename}</h3>
+          {currentPhoto.original_filename && currentPhoto.original_filename !== currentPhoto.filename && (
+            <p className="text-neutral-400 text-sm">Original: {currentPhoto.original_filename}</p>
+          )}
+          <div className="mb-4" />
 
           {/* Actions */}
           <div className="flex gap-2 mb-6">

frontend/src/services/photos.service.ts

@@ -3,6 +3,7 @@ import { api } from '../config/api';
 export interface AdminPhoto {
   id: number;
   filename: string;
+  original_filename?: string;
   path: string;
   url: string;
   thumbnail_url: string | null;