fix: lock upload button until tour redirect

tests/check-upload-button-state.php

@@ -0,0 +1,13 @@
+<?php
+/** Регрессия: до редиректа на Tour повторная загрузка блокируется для любого формата. */
+
+$form = (string) file_get_contents(dirname(__DIR__) . '/components/form.php');
+
+foreach (['function beginUploadPending', 'uploadDots', 'Загрузка', 'uploadPending'] as $needle) {
+    if (!str_contains($form, $needle)) {
+        fwrite(STDERR, "FAIL: preland uploader must contain {$needle}\n");
+        exit(1);
+    }
+}
+
+echo "OK: preland upload button state\n";