Fix multiple bugs: thumbnail generation, branding settings, categories, theme, feedback icons, upload limit, email errors

Bug fixes included:

#52 - Thumbnail Generation: Added proper parsing of settings values and validation
      of Sharp fit parameter to handle JSON-encoded strings correctly

#61 - Branding Settings Not Persisting: Added _parseBoolean helper for reliable
      boolean parsing, added hide_powered_by option for white-label support

#55 - Categories Not Applied: Fixed category update logic to properly handle
      numeric category IDs, added updated_at timestamp, improved cache invalidation

#59/#56 - Gallery Layout & Apply Theme: Set isPreviewMode=true so theme changes
      immediately propagate to parent state, hidden redundant Apply button

#58 - Feedback Icons Show When Disabled: Added feedbackEnabled check to comment
      and like buttons in MasonryGalleryLayout and GridGalleryLayout

#57 - Upload Limit 100MB: Increased body parser limit from 100MB to 500MB to
      support larger batch uploads

#54 - Wrong Error Message: Enhanced email error handling with specific error
      codes and translation keys for better user feedback

frontend/src/components/gallery/GalleryLayout.tsx

@@ -29,6 +29,7 @@ interface GalleryLayoutProps {
     logo_display_header?: boolean;
     logo_display_hero?: boolean;
     logo_display_mode?: 'logo_only' | 'text_only' | 'logo_and_text';
+    hide_powered_by?: boolean;
   };
   showLogout?: boolean;
   onLogout?: () => void;
@@ -438,7 +439,10 @@ export const GalleryLayout: React.FC<GalleryLayoutProps> = ({
             </p>
           )}
           <p className="text-xs sm:text-sm text-neutral-500">
-            {brandingSettings?.footer_text || '© 2024 Your Company. All rights reserved.'} | Powered by <span className="font-semibold">PicPeak</span>
+            {brandingSettings?.footer_text || '© 2024 Your Company. All rights reserved.'}
+            {!brandingSettings?.hide_powered_by && (
+              <> | Powered by <span className="font-semibold">PicPeak</span></>
+            )}
           </p>
           {brandingSettings?.company_name && brandingSettings?.company_tagline && (
             <p className="text-xs text-neutral-400 mt-2">