fix: 플레이어 스폰 위치 중복 문제 해결 — Round-Robin 순차 할당 도입

- PlayerSpawnPoint.GetRandomSpawnPoint()을 랜덤에서 Round-Robin 순차 할당으로 변경
- 접속 순서대로 스폰 포인트를 순환하며 중복 스폰 방지
- BalanceDummy 씬에 두 번째 스폰 포인트 추가 (x=-5, y=3, z=0)

Assets/Scenes/BalanceDummy.unity

@@ -4324,6 +4324,51 @@ PrefabInstance:
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     m_AddedComponents: []
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+  m_PrefabInstance: {fileID: 0}
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+  m_Component:
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+  - component: {fileID: 808329369}
+  m_Layer: 0
+  m_Name: SpawnPoint (2)
+  m_TagString: Untagged
+  m_Icon: {fileID: 0}
+  m_NavMeshLayer: 0
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+--- !u!114 &808329369
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+  m_Script: {fileID: 11500000, guid: aba9a2eb2571da14d901ed51c8866f47, type: 3}
+  m_Name: 
+  m_EditorClassIdentifier: Colosseum.Game::Colosseum.Network.PlayerSpawnPoint
+  useRotation: 1
+--- !u!4 &808329370
+Transform:
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+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
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+  serializedVersion: 2
+  m_LocalRotation: {x: 0, y: 0, z: 0, w: 1}
+  m_LocalPosition: {x: -5, y: 3, z: 0}
+  m_LocalScale: {x: 1, y: 1, z: 1}
+  m_ConstrainProportionsScale: 0
+  m_Children: []
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@@ -13610,3 +13655,4 @@ SceneRoots:
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+  - {fileID: 808329370}