Audit quick wins: null guard, API error toasts, aria-labels on suppress buttons

- app.js: guard events array with || [] before .filter() to prevent crash on null
- app.js: show warning toast when /api/network or /api/status fail (was silent)
- app.js: add aria-label to all dynamically-generated suppress buttons
- index.html: add aria-label to server-rendered suppress buttons

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

static/app.js

@@ -45,14 +45,14 @@ async function refreshAll() {
       updateUnifiTable(net.unifi || []);
       updateTopology(net.hosts || {});
     } else {
-      console.warn('Network API failed:', netResult.reason);
+      showToast('Network data unavailable', 'warning');
     }
     if (statusResult.status === 'fulfilled') {
       const status = statusResult.value;
       updateEventsTable(status.events || [], status.total_active);
       updateStatusBar(status.summary || {}, status.last_check || '', status.daemon_ok);
     } else {
-      console.warn('Status API failed:', statusResult.reason);
+      showToast('Status data unavailable', 'warning');
     }
   } finally {
     if (refreshBtn) refreshBtn.classList.remove('is-loading');
@@ -153,7 +153,8 @@ function updateUnifiTable(devices) {
       ? `<button class="lt-btn lt-btn-ghost lt-btn-sm btn-suppress"
             data-sup-type="unifi_device"
             data-sup-name="${lt.escHtml(d.name)}"
-            data-sup-detail="">🔕 Suppress</button>`
+            data-sup-detail=""
+            aria-label="Suppress alerts for ${lt.escHtml(d.name)}">🔕 Suppress</button>`
       : '';
     return `
       <tr class="${statusClass}">
@@ -171,7 +172,7 @@ function updateEventsTable(events, totalActive) {
   const wrap = document.getElementById('events-table-wrap');
   if (!wrap) return;
 
-  const active = events.filter(e => e.severity !== 'info');
+  const active = (events || []).filter(e => e.severity !== 'info');
   if (!active.length) {
     wrap.innerHTML = '<p class="empty-state">No active alerts ✔</p>';
     return;
@@ -207,7 +208,8 @@ function updateEventsTable(events, totalActive) {
           <button class="lt-btn lt-btn-ghost lt-btn-sm btn-suppress"
             data-sup-type="${lt.escHtml(supType)}"
             data-sup-name="${lt.escHtml(e.target_name)}"
-            data-sup-detail="${lt.escHtml(e.target_detail||'')}">🔕</button>
+            data-sup-detail="${lt.escHtml(e.target_detail||'')}"
+            aria-label="Suppress alert for ${lt.escHtml(e.target_name)}">🔕</button>
         </td>
       </tr>`;
   }).join('');