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/prisma/schema.prisma

@@ -181,6 +181,7 @@ model MealPlanEntry {
   date      DateTime @db.Date
   recipe    Recipe   @relation(fields: [recipeId], references: [id], onDelete: Cascade)
   recipeId  Int
+  servings  Int?
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt