make mentions clickable

src/system/helper/format.php

@@ -48,6 +48,7 @@ class Format {
 
   public static function post(string $text) {
 
+    $text = preg_replace("|@([a-zA-Z0-9_]+)|i", "<a href=\"follow/$1\">@$1</a>", $text);
     $text = preg_replace("|((https?://)?([\d\w\.-]+\.[\w\.]{2,6})[^\s\]\[\<\>]*/?)|i", "<a href=\"$1\" target=\"_blank\">$3</a>", $text);
     $text = nl2br($text);