feat(receipt-import): add rule-based category suggestion logic for items

feat(migrations): add new categories for lactose-free products and allergy options

backend/prisma/migrations/20260502135500_add_allergi_mejeri_matfett_l3/migration.sql

@@ -0,0 +1,15 @@
+-- Ensure L3 "Matfett" exists under:
+-- Mejeri, ost & ägg > Allergi mejeri
+
+INSERT INTO `Category` (`name`, `parentId`)
+SELECT 'Matfett', c2.id
+FROM `Category` c1
+JOIN `Category` c2
+  ON c2.parentId = c1.id
+  AND c2.name = 'Allergi mejeri'
+LEFT JOIN `Category` c3
+  ON c3.parentId = c2.id
+  AND c3.name = 'Matfett'
+WHERE c1.name = 'Mejeri, ost & ägg'
+  AND c1.parentId IS NULL
+  AND c3.id IS NULL;