fix: inspector.html stale/updated timestamp broken date parsing

Same bug as was just fixed in links.html: data.updated is stored as
"YYYY-MM-DD HH:MM:SS UTC" by monitor.py, so appending 'Z' produced
"…UTCZ" — an invalid date. The stale-data warning and Updated timestamp
in Inspector were silently showing "Invalid Date" and the stale overlay
never fired. Fixed to use _toIso() (already global via app.js).

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

templates/inspector.html

@@ -428,7 +428,7 @@ function renderInspector(data) {
 
   const updEl = document.getElementById('inspector-updated');
   if (updEl && data.updated) {
-    const updMs = new Date(data.updated + (data.updated.includes('Z') ? '' : 'Z'));
+    const updMs = new Date(_toIso(data.updated));
     const ageMin = (Date.now() - updMs) / 60000;
     const timeStr = updMs.toLocaleTimeString();
     if (ageMin > 15) {