fix: Use wp_signon for proper WordPress authentication in standalone login

admin-spa/src/routes/Login.tsx

@@ -37,6 +37,11 @@ export function Login() {
         window.WNW_CONFIG.currentUser = data.user;
         window.WNW_CONFIG.nonce = data.nonce;
         
+        // CRITICAL: Also update WNW_API.nonce for API requests
+        if (window.WNW_API) {
+          window.WNW_API.nonce = data.nonce;
+        }
+        
         // Redirect to dashboard (no reload needed, auth state is updated)
         navigate('/dashboard');
       } else {