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/confirm-action.tsx

@@ -0,0 +1,36 @@
+"use client";
+
+import type { ReactNode } from "react";
+
+export function ConfirmAction({
+  message,
+  action,
+  userId,
+  className,
+  style,
+  children,
+}: {
+  message: string;
+  action: string;
+  userId: number;
+  className?: string;
+  style?: React.CSSProperties;
+  children: ReactNode;
+}) {
+  return (
+    <form action="/api/admin/users/actions" method="post" style={{ display: "inline-block" }}>
+      <input type="hidden" name="userId" value={userId} />
+      <input type="hidden" name="action" value={action} />
+      <button
+        type="submit"
+        className={className}
+        style={style}
+        onClick={(e) => {
+          if (!confirm(message)) e.preventDefault();
+        }}
+      >
+        {children}
+      </button>
+    </form>
+  );
+}