fix(ui): refine glassmorphism and page transition animations

- Added custom light/dark background images to replace unsplash URLs.
- Enhanced active sidebar item shadow and backdrop blur for better visibility.
- Fixed double loading flickers on user, node, group, and panel-sharing pages.
- Removed opacity transitions from AnimatedPage to prevent backdrop-filter rendering issues during page navigation.

vite-frontend/src/pages/user.tsx

@@ -185,7 +185,7 @@ const normalizeUserTunnelItem = (item: Partial<UserTunnel>): UserTunnel => {
 export default function UserPage() {
   // 状态管理
   const [users, setUsers] = useState<User[]>([]);
-  const [loading, setLoading] = useState(false);
+  const [loading, setLoading] = useState(true);
   const [searchKeyword, setSearchKeyword] = useLocalStorageState(
     "user-search-keyword",
     "",
@@ -466,10 +466,6 @@ export default function UserPage() {
     void loadMonitorPermissions();
   }, [loadMonitorPermissions, loadSpeedLimits, loadTunnels, loadUserGroups]);
 
-  useEffect(() => {
-    void loadUsers();
-  }, [loadUsers]);
-
   useEffect(() => {
     if (searchDebounceRef.current) {
       clearTimeout(searchDebounceRef.current);