Add UI animations: dialogs, tabs, settings, browser stagger, banner pulse

- Dialog modals: scale+fade entrance/exit with animated backdrop
- Tab panels: fade-in with subtle slide on switch
- Settings sections: content slide-down on expand
- Browser grid/list items: staggered cascade entrance animation
- Connection banner: slide-in + attention pulse on disconnect
- Accessibility: prefers-reduced-motion disables all animations

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

media_server/static/js/browser.js

@@ -250,9 +250,10 @@ function renderBrowserList(items, container) {
         return;
     }
 
-    items.forEach(item => {
+    items.forEach((item, idx) => {
         const row = document.createElement('div');
         row.className = 'browser-list-item';
+        row.style.setProperty('--item-index', Math.min(idx, 20));
         row.dataset.name = item.name;
         row.dataset.type = item.type;
 
@@ -343,9 +344,10 @@ function renderBrowserGrid(items, container) {
         return;
     }
 
-    items.forEach(item => {
+    items.forEach((item, idx) => {
         const div = document.createElement('div');
         div.className = 'browser-item';
+        div.style.setProperty('--item-index', Math.min(idx, 20));
         div.dataset.name = item.name;
         div.dataset.type = item.type;
 
@@ -870,7 +872,7 @@ function showManageFoldersDialog() {
 }
 
 function closeFolderDialog() {
-    document.getElementById('folderDialog').close();
+    closeDialog(document.getElementById('folderDialog'));
 }
 
 async function saveFolder(event) {