feat(layout): add admin panel layout with sidebar and header

- Add Sidebar component with navigation items (dashboard, bookings, tournaments, pos, clients, memberships, reports, settings)
- Add Header component with SiteSwitcher and user info/logout
- Add SiteSwitcher component for SUPER_ADMIN multi-site selection
- Add admin layout wrapper with AuthProvider
- Add placeholder Dashboard page

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/components/layout/header.tsx

@@ -0,0 +1,40 @@
+'use client';
+
+import { useSession, signOut } from 'next-auth/react';
+import { LogOut } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import { SiteSwitcher } from './site-switcher';
+
+export function Header() {
+  const { data: session } = useSession();
+
+  const handleLogout = () => {
+    signOut({ callbackUrl: '/login' });
+  };
+
+  const userRole = session?.user?.role || '';
+  const displayRole = userRole
+    .replace(/_/g, ' ')
+    .toLowerCase()
+    .replace(/\b\w/g, (l) => l.toUpperCase());
+
+  return (
+    <header className="sticky top-0 z-30 flex h-16 items-center justify-between border-b border-primary-200 bg-white px-6 pl-64">
+      <div className="ml-6">
+        <SiteSwitcher />
+      </div>
+
+      <div className="flex items-center gap-4">
+        <div className="text-right">
+          <p className="text-sm font-medium text-primary-800">{session?.user?.name || 'Usuario'}</p>
+          <p className="text-xs text-primary-500">{displayRole}</p>
+        </div>
+        <Button variant="ghost" size="icon" onClick={handleLogout} title="Cerrar sesión">
+          <LogOut className="h-5 w-5" />
+        </Button>
+      </div>
+    </header>
+  );
+}
+
+export default Header;