Harden app for 24-7 offline-first operation

lib/features/home/unsplash_background.dart

@@ -96,6 +96,7 @@ class _UnsplashBackgroundState extends ConsumerState<UnsplashBackground> {
         // Soft opacity behind the MainScreen's dark glass vignette
         color: Colors.black.withValues(alpha: 0.5), 
         colorBlendMode: BlendMode.darken,
+        errorBuilder: (_, __, ___) => const SizedBox.shrink(),
       ),
     );
   }