fix: improve imageUrl handling in Recipe model to avoid null or empty values

flutter/Caddyfile

@@ -1,6 +1,11 @@
 :{$PORT:5000} {
     root * /usr/share/caddy
 
+    # Recipe images are stored in a shared volume and served by the Next service.
+    handle /images/* {
+        reverse_proxy recipe-frontend:3000
+    }
+
     # Proxy API calls to backend service on the internal Docker network.
     handle /api/* {
         reverse_proxy recipe-api:8080

flutter/lib/features/recipes/domain/recipe.dart

@@ -26,12 +26,16 @@ class Recipe {
     final dynamic rawImageUrl = json['imageUrl'];
     final dynamic rawServings = json['servings'];
     final rawIngredients = json['ingredients'] as List<dynamic>? ?? [];
+    final normalizedImageUrl = rawImageUrl?.toString().trim();
 
     return Recipe(
       id: rawId is num ? rawId.toInt() : int.parse(rawId.toString()),
       title: (rawTitle ?? '').toString(),
       description: rawDescription == null ? null : rawDescription.toString(),
-      imageUrl: rawImageUrl == null ? null : rawImageUrl.toString(),
+      imageUrl:
+        (normalizedImageUrl == null || normalizedImageUrl.isEmpty)
+          ? null
+          : normalizedImageUrl,
       servings: rawServings == null
           ? null
           : (rawServings is num