fix: TestConnection for unsaved servers, traffic display, and cache-busting

- Use $params['serverhostname']/serverpassword directly in TestConnection
  instead of database lookup (serverid=0 is falsy for new servers)
- Default traffic "Used" to 0 GB when allocated but no usage reported
- Add ?v=0.0.19 cache-busting to JS/CSS includes in overview.tpl

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/servers/VirtFusionDirect/lib/ServerResource.php

@@ -21,6 +21,8 @@ class ServerResource
         $trafficUsed = '-';
         if (isset($server['usage']['traffic']['used'])) {
             $trafficUsed = round($server['usage']['traffic']['used'] / 1073741824, 2) . ' GB';
+        } elseif (isset($server['settings']['resources']['traffic']) && $server['settings']['resources']['traffic'] > 0) {
+            $trafficUsed = '0 GB';
         }
 
         $data = [