Add skeleton templates for various sections

- Created skeleton templates for events, notifications, plugins, presence, report, settings, and workflows to enhance loading states.
- Implemented structured skeletons for tab details, tab events, maintenance backup, database tools, logging, multi-edit, presence, sessions, and system info.
- Each template includes shimmer effects for loading indicators, improving user experience during data fetching.

front/pluginsCore.php

@@ -516,6 +516,7 @@ function generateTabs() {
   if (visiblePlugins.length === 0) {
     $('#tabs-content-location').html(`<p class="text-muted" style="padding: 15px;">${getString('Gen_No_Data')}</p>`);
     hideSpinner();
+    hidePluginsSkeleton();
     return;
   }
 
@@ -534,6 +535,7 @@ function generateTabs() {
   }
 
   hideSpinner()
+  hidePluginsSkeleton()
 }
 
 function resetTabs() {
@@ -858,4 +860,12 @@ else
   initFields();
 }
 
+function hidePluginsSkeleton() {
+  $('#plugins-skeleton').fadeOut(250, function() { $(this).remove(); });
+}
+
+window.addEventListener('load', function() {
+  setTimeout(hidePluginsSkeleton, 15000);
+});
+
 </script>