fix(dashboard): smooth latency badge updates, add ping settings

- Snapshot and restore latency badge values across innerHTML re-renders
  so badges never flash back to "…ms" on the 2-second state refresh cycle
- Add CSS transition (color 0.4s ease) and in-flight opacity dim (.pinging)
  to .latency-badge for smooth color changes
- Decouple latency pinging from the state refresh cycle — pings now run on
  their own independent interval instead of being triggered by refresh()
- Add two new settings under a "Latency Ping" section in Settings:
  - Enable Latency Ping toggle (latencyPingEnabled, default: true)
  - Ping Interval in seconds (latencyPingIntervalMs, default: 5s)
- Restart ping interval immediately on settings save so changes take effect
  without a page reload

extension/dashboard/pages/service-tunnels.js

@@ -30,6 +30,12 @@ function updateServiceTunnelsTable(state) {
   const countEl = $('serviceTunnelCount');
   if (countEl) countEl.textContent = tunnels.length;
 
+  // Snapshot latency badge values before re-render so they survive the innerHTML swap
+  const _latencySnapshot = {};
+  tbody.querySelectorAll('.latency-badge[data-ping-port]').forEach(b => {
+    _latencySnapshot[b.dataset.pingHost + ':' + b.dataset.pingPort] = { text: b.textContent, color: b.style.color };
+  });
+
   if (tunnels.length === 0) {
     tbody.innerHTML = `
       <tr><td colspan="6">
@@ -95,6 +101,15 @@ function updateServiceTunnelsTable(state) {
       </tr>`;
   }).join('');
 
+  // Restore latency badge values immediately so there's no flash back to "…ms"
+  tbody.querySelectorAll('.latency-badge[data-ping-port]').forEach(b => {
+    const snap = _latencySnapshot[b.dataset.pingHost + ':' + b.dataset.pingPort];
+    if (snap && snap.text && snap.text !== '…ms') {
+      b.textContent = snap.text;
+      b.style.color = snap.color;
+    }
+  });
+
   tbody.querySelectorAll('.svc-row-cb').forEach(cb => {
     cb.addEventListener('change', _updateSvcBulkBar);
   });