Product Details Controller (customer)

Customer-side controller for ProductDetailScreen. Holds the Product, currently selected options + resolved variant, quantity, isFavorite. _resolveVariant matches the selected options against product.variants and clears the variant when none match.

1. setFromProduct seeds the state with the Product passed via route extra, auto-selecting the first value of each option.
2. loadProduct(id) is the fallback path when the user deep-links without an extra — calls MarketplaceService.getProductById.
3. selectOption mutates selectedOptions and re-resolves the variant.
4. toggleFavorite mirrors into marketplaceControllerProvider so the parent list stays in sync.

• If no variant matches the current option combination, selectedVariant is cleared — the Add-to-cart button must disable.
• Quantity has a floor of 1; UI 'minus' button hides below that.
• isFavorite is local-only in this controller — the wishlist service is what persists it.

• lib/src/features/shared/product_details/controllers/product_details_controller.dart:5 // ProductDetailsState
• lib/src/features/shared/product_details/controllers/product_details_controller.dart:50 // ProductDetailsController
• lib/src/features/shared/product_details/controllers/product_details_controller.dart:78 // loadProduct
• lib/src/features/shared/product_details/controllers/product_details_controller.dart:115 // _resolveVariant

copyWith uses a `clearVariant` bool to explicitly null selectedVariant — copyWith's normal ?? pattern can't express 'set to null' otherwise.