Add pregame lobby with live chat

Players used to get bounced back to the dashboard when a session
wasn't full yet. Now they land on a lobby page showing who has
joined, and can chat with each other while waiting - messages are
broadcast live over the existing Mercure hub, and the session
auto-starts (and the lobby notifies everyone) once it fills up.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/Game/GameDashboardServiceTest.php

@@ -10,6 +10,7 @@ use App\Game\Entity\SessionSetting;
 use App\Game\Enum\GameStatus;
 use App\Game\Enum\SessionStatus;
 use App\Game\Enum\SessionSettingType;
+use App\Game\Repository\LobbyMessageRepository;
 use App\Game\Service\GameDashboardService;
 use App\Tech\Entity\User;
 use Doctrine\ORM\EntityManagerInterface;
@@ -23,6 +24,7 @@ class GameDashboardServiceTest extends TestCase
     private $entityManager;
     private $gameRepository;
     private $sessionRepository;
+    private $lobbyMessageRepository;
     private $hub;
     private $service;
 
@@ -31,14 +33,15 @@ class GameDashboardServiceTest extends TestCase
         $this->entityManager = $this->createMock(EntityManagerInterface::class);
         $this->gameRepository = $this->createMock(GameRepository::class);
         $this->sessionRepository = $this->createMock(SessionRepository::class);
+        $this->lobbyMessageRepository = $this->createMock(LobbyMessageRepository::class);
         $this->hub = $this->createMock(HubInterface::class);
 
         $this->service = new GameDashboardService(
             $this->gameRepository,
             $this->sessionRepository,
+            $this->lobbyMessageRepository,
             $this->entityManager,
             $this->hub,
-            'http://localhost/topic'
         );
     }