feat(shopping): add week-based shopping list repository query

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

backend/src/main/java/com/recipeapp/shopping/ShoppingListRepository.java

@@ -3,7 +3,10 @@ package com.recipeapp.shopping;
 import com.recipeapp.shopping.entity.ShoppingList;
 import org.springframework.data.jpa.repository.JpaRepository;
 
+import java.time.LocalDate;
+import java.util.Optional;
 import java.util.UUID;
 
 public interface ShoppingListRepository extends JpaRepository<ShoppingList, UUID> {
+    Optional<ShoppingList> findByHouseholdIdAndWeekPlanWeekStart(UUID householdId, LocalDate weekStart);
 }