fix: 限制有效签名名称唯一并保留批量导入补资料

api/prisma/schema.prisma

@@ -776,6 +776,8 @@ model ReportNotificationRead {
 }
 
 model SmsSignature {
+  // Active name uniqueness (including null applicationId) is enforced by two partial SQL indexes.
+  // Owned by migration 20260917120000_signature_active_name_unique; do not replace with @@unique.
   id              String   @id @default(cuid())
   tenantId        String
   applicationId   String?