fix: resolve webhook notification timestamp error and improve scroll timing

- Fix RangeError in AlertManager by using correct timestamp fields (triggeredAt/lastUpdate) instead of non-existent alert.timestamp
- Replace Promise.resolve() with requestAnimationFrame() for better scroll position restoration timing

🤖 Generated with [Claude Code](https://claude.ai/code)

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

server/alertManager.js

@@ -1234,7 +1234,7 @@ This alert was generated by Pulse monitoring system.
         };
 
         const payload = {
-            timestamp: new Date(alert.timestamp).toISOString(),
+            timestamp: new Date(alert.triggeredAt || alert.lastUpdate || Date.now()).toISOString(),
             alert: {
                 id: alert.id,
                 rule: {

src/public/js/utils.js

@@ -299,8 +299,8 @@ PulseApp.utils = (() => {
         // Execute the update function
         updateFn();
 
-        // Restore scroll positions after a microtask to ensure DOM is updated
-        Promise.resolve().then(() => {
+        // Restore scroll positions after DOM updates are complete
+        requestAnimationFrame(() => {
             element.scrollLeft = scrollLeft;
             element.scrollTop = scrollTop;
         });