feat(migration): enforce ownerId requirement in Product table

- Removed all products without an owner to maintain data integrity.
- Updated ownerId column to be non-nullable.
- Modified foreign key constraint for ownerId to use ON DELETE CASCADE.

backend/prisma/migrations/20260502160000_product_owner_required/migration.sql

@@ -0,0 +1,17 @@
+-- Steg 1: Ta bort alla produkter utan ägare (globala seed-produkter)
+-- Detta tar automatiskt bort relaterade rader via ON DELETE CASCADE
+-- för: InventoryItem, PantryItem, ReceiptAlias, ProductTag, Nutrition, UserProduct
+DELETE FROM `Product` WHERE `ownerId` IS NULL;
+
+-- Steg 2: Gör ownerId obligatoriskt
+ALTER TABLE `Product`
+  MODIFY COLUMN `ownerId` INT NOT NULL;
+
+-- Steg 3: Uppdatera foreign key constraint till CASCADE (ta bort gammal, lägg till ny)
+ALTER TABLE `Product`
+  DROP FOREIGN KEY IF EXISTS `Product_ownerId_fkey`;
+
+ALTER TABLE `Product`
+  ADD CONSTRAINT `Product_ownerId_fkey`
+  FOREIGN KEY (`ownerId`) REFERENCES `User`(`id`)
+  ON DELETE CASCADE ON UPDATE CASCADE;