Replace app.html with dum_3D_slunce.html in index.php for updated content delivery

locenice/index.php

@@ -1,3 +1,10 @@
 <?php
-
-readfile(__DIR__ . '/dum_3D_slunce.html');
+// Upload this whole folder, not only this file. No Node.js or database required.
+header('Content-Type: text/html; charset=utf-8');
+header('X-Content-Type-Options: nosniff');
+$file = __DIR__ . '/app.html';
+if (!is_readable($file)) {
+    http_response_code(500);
+    exit('Chybi app.html. Nahrajte celou slozku locenice.');
+}
+readfile($file);