feat(meal-plan): add servings field to MealPlanEntry and update related functionality

feat(products): implement bulk update for product categories

feat(recipes): add servings input to WriteRecipePage and update MealPlanClient for servings management

refactor(types): enhance Product and Category types with additional properties

backend/src/products/products.service.ts

@@ -397,4 +397,14 @@ export class ProductsService {
     ]);
     return { ok: true };
   }
+
+  async bulkUpdate(ids: number[], data: { categoryId?: number | null }) {
+    const updateData: Record<string, any> = {};
+    if ('categoryId' in data) {
+      updateData.categoryId = data.categoryId;
+    }
+    if (Object.keys(updateData).length === 0) return { updated: 0 };
+    await this.prisma.product.updateMany({ where: { id: { in: ids } }, data: updateData });
+    return { updated: ids.length };
+  }
 }