refac: missing user or article is reported with a domain not-found error instead of a raw GORM error, and the API answers 404 for it

internal/infrastructure/persistence/repositories/notFound.go

@@ -0,0 +1,14 @@
+package persistence
+
+import (
+	"errors"
+
+	"gorm.io/gorm"
+)
+
+func mapNotFoundErr(err error, sentinel error) error {
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return sentinel
+	}
+	return err
+}