feat: redesign admin panel with Lucide icons and modern styling

- Add lucide-react for SVG icons throughout the admin
- Redesign sidebar with gradient background, icons per nav item, and sticky layout
- Redesign topbar with cleaner user info display
- Redesign dashboard with icon-backed stat cards, gradient progress bars, activity feed
- Update AdminNavLink with icon support and new active state styling
- Improve table styling in admin-page CSS (rounded corners, hover, spacing)
- Clean up unused admin CSS

src/components/admin/admin-nav-link.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import Link from "next/link";
+import type { ReactNode } from "react";
 import { usePathname } from "next/navigation";
 
 /**
@@ -8,7 +9,7 @@ import { usePathname } from "next/navigation";
  * exactly; every other entry also matches its sub-routes (e.g. /admin/radio is
  * active on /admin/radio/history) so the current section stays lit.
  */
-export function AdminNavLink({ href, label }: { href: string; label: string }) {
+export function AdminNavLink({ href, icon, children }: { href: string; icon?: ReactNode; children: ReactNode }) {
   const pathname = usePathname() ?? "";
   const active =
     href === "/admin" ? pathname === "/admin" : pathname === href || pathname.startsWith(`${href}/`);
@@ -16,11 +17,18 @@ export function AdminNavLink({ href, label }: { href: string; label: string }) {
   return (
     <Link
       href={href}
-      className={`flex items-center gap-2 px-2.5 py-1.5 rounded-lg text-[#c8cbe0] text-sm font-semibold no-underline transition-[background,color] duration-150 hover:bg-white/7 hover:text-white hover:no-underline ${
-        active ? "bg-[var(--color-primary)] text-[#1a1a2e] shadow-[0_2px_8px_rgba(238,180,37,0.35)]" : ""
+      className={`flex items-center gap-2.5 px-2.5 py-2 rounded-xl text-sm font-medium no-underline transition-all duration-150 ${
+        active
+          ? "bg-gradient-to-r from-[var(--color-primary)]/20 to-transparent text-white shadow-sm border-l-2 border-[var(--color-primary)]"
+          : "text-[#8b8fa8] hover:text-white hover:bg-white/[0.04] hover:no-underline"
       }`}
     >
-      {label}
+      {icon ? (
+        <span className={`flex-none ${active ? "text-[var(--color-primary)]" : "text-[#5c5f7a]"}`}>
+          {icon}
+        </span>
+      ) : null}
+      <span>{children}</span>
     </Link>
   );
 }