feat(ui): Repeat xd-client UI with modern adaptive features

- Integrated Tailwind CSS v4 and Shadcn UI components from xd-client
- Adopted xd-client modern aesthetic (oklch, radial gradients, glassmorphism)
- Combined with modern adaptive 3-tier navigation logic
- Refactored all pages (Profile, Login, Settings, Messages, Schedule, Grades, Debts)
- Enhanced ThemeProvider with dynamic Material You palette generation
- Polished overall UX and animations

Refs #3
Co-Authored-By: Claude <noreply@anthropic.com>

src/components/ui/skeleton.tsx

@@ -0,0 +1,13 @@
+import { cn } from "@/lib/utils";
+
+function Skeleton({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="skeleton"
+      className={cn("animate-pulse rounded-md bg-muted/80", className)}
+      {...props}
+    />
+  );
+}
+
+export { Skeleton };