Supprime les mini-jeux (survival/teams), corrige tous les bugs identifiés

- Supprime DeathZone.cs, ZoneCapture.cs, ArenaZoneBuilder.cs
- ArenaRoom.js : mode race uniquement, fix _checkRoundEndCondition, fix _getActiveCount
- GameState.js : supprime team (Player) et deathZoneY/teamScoreRed/teamScoreBlue (GameState)
- NetworkSchema.cs : aligne sur le nouveau schéma serveur (supprime team, indices corrigés)
- NetworkManager.cs : supprime OnDeathZoneYChanged/SendDeathZoneHit/SendInZone, OnRoundStart passe totalRounds
- GameManager.cs : subscriptions OnEnable→Start/OnDestroy, fix Lobby (player visible si connecté), HandleRoundStart(totalRounds)
- GameHUD.cs : supprime blocs survival/teams, ajoute SetTotalRounds, supprime dead code
- PlayerController.cs : cache Rigidbody, fix OnCollisionStay gel (supprime else), SetSpawnPosition
- CheckpointSystem.cs : flash le prochain checkpoint actif, supprime FinishFlash vide
- LobbyUI.cs : CancelInvoke sur connexion, appelle SetSpawnPosition

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

game/Assets/Scripts/Network/LobbyUI.cs

@@ -88,6 +88,7 @@ public class LobbyUI : MonoBehaviour
         _lobbyActive = false;
         _isConnecting = false;
         _statusMessage = "";
+        CancelInvoke(nameof(CheckConnectionTimeout));
 
         // --- Activate the player hierarchy ---
         if (playerRoot != null)
@@ -113,6 +114,7 @@ public class LobbyUI : MonoBehaviour
                         rb.position = spawnPos;
                     }
                     pc.transform.position = spawnPos;
+                    pc.SetSpawnPosition(spawnPos);
                     Debug.Log($"[Lobby] Player teleported to spawn: {spawnPos}");
                 }
                 pc.enabled = true;