Restore 204 response for login and logout endpoints

The fix from PR #1061 (076865d) returned 204 No Content from
login() and logout() to signal navigation completion to WebDriver.
This was present on 7.x but lost during the 8.x branch creation,
causing intermittent loginAs() failures (#1152) and favicon 404s.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Josh Salway

src/Http/Controllers/UserController.php

@@ -33,7 +33,7 @@ public function user($guard = null)
      *
      * @param  string  $userId
      * @param  string|null  $guard
-     * @return void
+     * @return \Illuminate\Http\Response
      */
     public function login($userId, $guard = null)
     {
@@ -46,13 +46,15 @@ public function login($userId, $guard = null)
                     : $provider->retrieveById($userId);
 
         Auth::guard($guard)->login($user);
+
+        return response(status: 204);
     }
 
     /**
      * Log the user out of the application.
      *
      * @param  string|null  $guard
-     * @return void
+     * @return \Illuminate\Http\Response
      */
     public function logout($guard = null)
     {
@@ -61,6 +63,8 @@ public function logout($guard = null)
         Auth::guard($guard)->logout();
 
         Session::forget('password_hash_'.$guard);
+
+        return response(status: 204);
     }
 
     /**