feat(shop): move linked fee configuration to product level

shop/supabase/migrations/20260722110000_move_linked_fee_to_products.sql

@@ -0,0 +1,7 @@
+-- Remove linked_fee_product_id from product_modules
+ALTER TABLE public.product_modules 
+DROP COLUMN IF EXISTS linked_fee_product_id;
+
+-- Add linked_fee_product_id to products
+ALTER TABLE public.products 
+ADD COLUMN IF NOT EXISTS linked_fee_product_id UUID REFERENCES public.products(id) ON DELETE SET NULL;