refactor: modularize AdminClientWrapper by extracting components

- Removed unused imports and components from AdminClientWrapper.
- Introduced AdminHeader, AdminOverviewCards, AdminFilters, and AdminContentTabs for better code organization and readability.
- Streamlined the layout and functionality of the admin dashboard, enhancing maintainability.

components/admin/admin-header.tsx

@@ -0,0 +1,23 @@
+"use client";
+
+import { Building2 } from "lucide-react";
+
+export function AdminHeader() {
+  return (
+    <div className="text-center space-y-4 mb-12">
+      <div className="inline-flex items-center gap-2 px-4 py-2 rounded-full bg-white/5 border border-white/10 backdrop-blur-sm">
+        <Building2 className="h-4 w-4 text-blue-400" />
+        <span className="text-sm font-medium text-slate-200">
+          Administration
+        </span>
+      </div>
+
+      <h1 className="text-4xl font-bold text-white">Dashboard Managérial</h1>
+
+      <p className="text-slate-400 max-w-2xl mx-auto leading-relaxed">
+        Vue d'ensemble des compétences par équipe et direction pour pilotage
+        stratégique
+      </p>
+    </div>
+  );
+}