fix: watermark thumbnails, custom logo display, and German translations

- Fix thumbnail display when watermarks enabled globally on existing galleries
  - Backend: Apply watermarks to thumbnails at the thumbnail endpoint
  - Frontend: Remove hack that redirected thumbnails to photo endpoint
- Fix custom logo display in gallery hero sections
  - Only apply brightness/invert filter to default PicPeak logo
  - Custom logos now display as-is with drop-shadow only
- Add German translations for Event Creation and Image Protection settings
  - settings.events: Pflichtfelder, Kundenname/E-Mail erforderlich, etc.
  - settings.imageSecurity: Bildschutz, Ratenbegrenzung, Sicherheitsüberwachung
  - Protection level options in both EN and DE locales

frontend/src/components/gallery/GalleryLayout.tsx

@@ -366,7 +366,10 @@ export const GalleryLayout: React.FC<GalleryLayoutProps> = ({
                     className={`${heroLogoSize.className} w-auto object-contain mx-auto`}
                     style={{
                       ...(heroLogoSize.style || {}),
-                      filter: 'brightness(0) invert(1) drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3))'
+                      // Only apply brightness/invert filter to default logo; custom logos display as-is
+                      filter: brandingSettings?.logo_url
+                        ? 'drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3))'
+                        : 'brightness(0) invert(1) drop-shadow(0 2px 4px rgba(0, 0, 0, 0.3))'
                     }}
                   />
                   {shouldShowCompanyName() && brandingSettings?.company_name && (

frontend/src/components/gallery/GalleryView.tsx

@@ -380,12 +380,12 @@ export const GalleryView: React.FC<GalleryViewProps> = ({ slug, event }) => {
       }
     });
     
-    // Transform URLs for watermarks if enabled
+    // Transform full-size URLs for watermarks if enabled
+    // Note: Thumbnails are watermarked server-side at the thumbnail endpoint
     if (watermarkEnabled) {
       photos = photos.map(photo => ({
         ...photo,
-        url: `/gallery/${slug}/photo/${photo.id}`,
-        thumbnail_url: `/gallery/${slug}/photo/${photo.id}` // Use watermarked version for thumbnails too
+        url: `/gallery/${slug}/photo/${photo.id}`
       }));
     }
     

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

@@ -142,8 +142,11 @@ export const HeroGalleryLayout: React.FC<HeroGalleryLayoutProps> = ({
                 } 
                 alt="Event logo" 
                 className="h-20 sm:h-24 lg:h-32 mx-auto"
-                style={{ 
-                  filter: 'brightness(0) invert(1) drop-shadow(0 4px 6px rgba(0, 0, 0, 0.5))'
+                style={{
+                  // Only apply brightness/invert filter to default logo; custom logos display as-is
+                  filter: eventLogo
+                    ? 'drop-shadow(0 4px 6px rgba(0, 0, 0, 0.5))'
+                    : 'brightness(0) invert(1) drop-shadow(0 4px 6px rgba(0, 0, 0, 0.5))'
                 }}
               />
             </div>