refactor: simplify duplicate account error detection

Replace dual string check with single unique identifier for more precise error handling

src/views/ImportAccountView.vue

@@ -245,10 +245,7 @@ export default class ImportAccountView extends Vue {
       // Check if this is a duplicate account error from saveNewIdentity
       const errorMessage =
         error instanceof Error ? error.message : String(error);
-      if (
-        errorMessage.includes("already exists") &&
-        errorMessage.includes("Cannot import duplicate account")
-      ) {
+      if (errorMessage.includes("Cannot import duplicate account")) {
         this.notify.warning(
           NOTIFY_DUPLICATE_ACCOUNT_IMPORT.message,
           TIMEOUTS.LONG,