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/Race/CheckpointSystem.cs

@@ -80,11 +80,10 @@ public class CheckpointSystem : MonoBehaviour
         {
             _finished = true;
             Debug.Log("[Checkpoint] FINISH LINE reached!");
-            StartCoroutine(FinishFlash());
         }
         else
         {
-            StartCoroutine(FlashCheckpoint(index));
+            StartCoroutine(FlashCheckpoint(_localCheckpointIndex));
         }
     }
 
@@ -146,17 +145,6 @@ public class CheckpointSystem : MonoBehaviour
         }
     }
 
-    private IEnumerator FinishFlash()
-    {
-        float t = 0f;
-        while (t < 2f)
-        {
-            t += Time.deltaTime;
-            yield return null;
-        }
-        // Finish confirmed via network — GameManager/EliminationOverlay handles the "Qualifié!" overlay
-    }
-
     private static void SetRendererColor(Renderer rend, Color c)
     {
         if (rend.material.HasProperty("_BaseColor")) rend.material.SetColor("_BaseColor", c);