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/RecipeDetailResponse.java

@@ -10,7 +10,6 @@ public record RecipeDetailResponse(
         short serves,
         short cookTimeMin,
         String effort,
-        boolean isChildFriendly,
         String heroImageUrl,
         List<IngredientItem> ingredients,
         List<StepItem> steps,