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/components/animated-page.tsx

@@ -13,10 +13,10 @@ export const AnimatedPage = ({
   className?: string;
 }) => (
   <motion.div
-    animate={{ opacity: 1, y: 0 }}
+    animate={{ y: 0 }}
     className={className}
-    exit={{ opacity: 0, y: -8 }}
-    initial={{ opacity: 0, y: 16 }}
+    exit={{ y: -8 }}
+    initial={{ y: 16 }}
     transition={{ duration: 0.28, ease: [0.25, 0.46, 0.45, 0.94] }}
   >
     {children}
@@ -28,9 +28,8 @@ export const AnimatedPage = ({
  * Children should use `staggerItem` as their `variants` prop.
  */
 export const staggerContainer = {
-  hidden: { opacity: 0 },
+  hidden: {},
   show: {
-    opacity: 1,
     transition: {
       staggerChildren: 0.05,
       delayChildren: 0.05,
@@ -42,9 +41,8 @@ export const staggerContainer = {
  * Individual stagger item variant — fade-in + slide-up.
  */
 export const staggerItem = {
-  hidden: { opacity: 0, y: 12 },
+  hidden: { y: 12 },
   show: {
-    opacity: 1,
     y: 0,
     transition: { duration: 0.25, ease: [0.25, 0.46, 0.45, 0.94] },
   },