Fix admin panel authentication and navigation for static export

- Replace router.push with window.location.href for reliable redirects
- Fix auth check to wait for component mount before accessing localStorage
- Ensure proper redirect after successful login
- Fix redirect behavior on all admin pages (dashboard, colors, requests)

app/upadaj/page.tsx

@@ -32,8 +32,8 @@ export default function AdminLogin() {
       // Track successful login
       trackEvent('Admin', 'Login', 'Success');
 
-      // Redirect to admin dashboard
-      router.push('/upadaj/dashboard');
+      // Redirect to admin dashboard using window.location for static export
+      window.location.href = '/upadaj/dashboard';
     } catch (err: any) {
       setError('Neispravno korisničko ime ili lozinka');
       console.error('Login error:', err);