fix: inspector stale data warning, remove dead supported_modes code

- inspector.html: show orange '⚠ Stale: HH:MM' with tooltip when link_stats data is >15 min old (previously just showed the time with no visual warning)
- style.css: add .g-stale-warn helper class (orange, bold) for the stale indicator
- diagnose.py: remove supported_modes accumulation from parse_ethtool() — field was collected but never consumed by analyze() or displayed anywhere

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

diagnose.py

@@ -221,8 +221,6 @@ class DiagnosticsRunner:
                 data['auto_neg'] = (val.lower() == 'on')
             elif key == 'Link detected':
                 data['link_detected'] = (val.lower() == 'yes')
-            elif 'Supported link modes' in key:
-                data.setdefault('supported_modes', []).append(val)
         return data
 
     @staticmethod

static/style.css

@@ -217,6 +217,7 @@
 .sev-pills          { display: flex; gap: 4px; }
 .g-page-sub { font-size: .78em; color: var(--text-muted); margin-top: 4px; }
 .g-page-sub-aside { font-size: .78em; color: var(--text-muted); margin-left: 8px; }
+.g-stale-warn { color: var(--orange); font-weight: 600; }
 
 /* ── Badge severity color variants (used with lt-badge) ───────────── */
 .badge-critical { color: var(--red);    border-color: var(--red);    text-shadow: var(--glow-red); }

templates/inspector.html

@@ -428,7 +428,14 @@ function renderInspector(data) {
 
   const updEl = document.getElementById('inspector-updated');
   if (updEl && data.updated) {
-    updEl.textContent = 'Updated: ' + new Date(data.updated + (data.updated.includes('Z') ? '' : 'Z')).toLocaleTimeString();
+    const updMs = new Date(data.updated + (data.updated.includes('Z') ? '' : 'Z'));
+    const ageMin = (Date.now() - updMs) / 60000;
+    const timeStr = updMs.toLocaleTimeString();
+    if (ageMin > 15) {
+      updEl.innerHTML = `<span class="g-stale-warn" title="Data is ${Math.floor(ageMin)} minutes old — monitor may be down">⚠ Stale: ${timeStr}</span>`;
+    } else {
+      updEl.textContent = 'Updated: ' + timeStr;
+    }
   }
 
   if (!Object.keys(switches).length) {