Cart Provider Wiring

Two NotifierProviders are exported: cartControllerProvider (the local cart list) and cartSelectionProvider (the selected variantIds). The backend CartService is plain — instantiated where needed; not provider-wrapped today.

1. cartControllerProvider builds with currentCustomerIdProvider as a watched dependency.
2. cartSelectionProvider builds with cartControllerProvider as a watched dependency.
3. Consumers (CartScreen, CheckoutScreen, AddToCart buttons) ref.watch / ref.read these providers directly.
4. CartService is constructed inline in CheckoutController and other consumers — no provider gate.

• Adding a provider for CartService would let tests inject a mock — currently not done.
• Provider disposal is implicit — they live for the app lifetime since nothing else holds a parent scope.

• lib/src/features/shared/cart/controllers/cart_controller.dart:130 // cartControllerProvider
• lib/src/features/shared/cart/controllers/cart_selection_controller.dart:30 // cartSelectionProvider

currentCustomerIdProvider lives in profile/personal_info_provider.dart — see the profile feature for its definition.