db: add allow_update_discount column to categories table

shop/supabase/migrations/20260710002000_add_allow_update_discount_to_categories.sql

@@ -0,0 +1,6 @@
+-- Migration: Add allow_update_discount to categories
+-- Purpose: Add a boolean flag to categories to control if their products are eligible for the update discount.
+
+ALTER TABLE public.categories ADD COLUMN IF NOT EXISTS allow_update_discount BOOLEAN DEFAULT true NOT NULL;
+
+NOTIFY pgrst, 'reload schema';