fix statusIntervalId redeclaration error on SPA re-navigation

Use var instead of let for statusIntervalId so the script can be
re-executed by the SPA script-cloning logic without throwing a
redeclaration error when navigating back to the status page.

https://claude.ai/code/session_01FUhPqQLahEoL6FMxhXkDKa

src/static/js/status.js

@@ -236,7 +236,7 @@ function refreshStatus() {
 /**
  * Initialize on page load
  */
-let statusIntervalId = null;
+var statusIntervalId = null;
 
 function initStatusPage() {
   // Clear any existing interval from a previous SPA navigation