refactor(recipes): drop is_child_friendly column and remove from all layers

V025 migration drops the column. Removed from Recipe entity, RecipeDetailResponse,
RecipeSummaryResponse, RecipeRepository JPQL, RecipeService, and RecipeController.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/com/recipeapp/recipe/dto/RecipeSummaryResponse.java

@@ -8,6 +8,5 @@ public record RecipeSummaryResponse(
         short serves,
         short cookTimeMin,
         String effort,
-        boolean isChildFriendly,
-        String heroImageUrl
+        String heroImagePreview
 ) {}