feat: 플레이어 관전 시스템 추가

- PlayerSpectator: 사망한 플레이어가 살아있는 플레이어 관찰
- PlayerCamera: SetTarget/ResetToPlayer/SnapToTarget 메서드 추가
- PlayerMovement: OnEnable/OnDisable에서 입력 액션 관리
- Tab 키로 관전 대상 전환 기능

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Assets/Scripts/Player/PlayerSpectator.cs

@@ -0,0 +1,195 @@
+using System.Collections.Generic;
+using UnityEngine;
+using Colosseum.Player;
+
+namespace Colosseum.Player
+{
+    /// <summary>
+    /// 플레이어 관전 시스템.
+    /// 사망한 플레이어가 살아있는 플레이어를 관찰할 수 있게 합니다.
+    /// </summary>
+    public class PlayerSpectator : MonoBehaviour
+    {
+        [Header("References")]
+        [Tooltip("PlayerCamera 컴포넌트")]
+        [SerializeField] private PlayerCamera playerCamera;
+
+        [Tooltip("PlayerNetworkController 컴포넌트")]
+        [SerializeField] private PlayerNetworkController networkController;
+
+        [Header("Spectate Settings")]
+        [Tooltip("관전 대상 전환 키")]
+        [SerializeField] private KeyCode nextTargetKey = KeyCode.Tab;
+
+        [Tooltip("관전 UI 표시 여부")]
+        [SerializeField] private bool showSpectateUI = true;
+
+        // 관전 상태
+        private bool isSpectating = false;
+        private int currentSpectateIndex = 0;
+        private List<PlayerNetworkController> alivePlayers = new List<PlayerNetworkController>();
+
+        // 이벤트
+        public event System.Action<bool> OnSpectateModeChanged; // (isSpectating)
+        public event System.Action<PlayerNetworkController> OnSpectateTargetChanged;
+
+        // Properties
+        public bool IsSpectating => isSpectating;
+        public PlayerNetworkController CurrentTarget => alivePlayers.Count > currentSpectateIndex ? alivePlayers[currentSpectateIndex] : null;
+
+        private void Awake()
+        {
+            // 컴포넌트 자동 참조
+            if (playerCamera == null)
+                playerCamera = GetComponent<PlayerCamera>();
+            if (networkController == null)
+                networkController = GetComponentInParent<PlayerNetworkController>();
+        }
+
+        private void Start()
+        {
+            if (networkController != null)
+            {
+                networkController.OnDeathStateChanged += HandleDeathStateChanged;
+            }
+        }
+
+        private void OnDestroy()
+        {
+            if (networkController != null)
+            {
+                networkController.OnDeathStateChanged -= HandleDeathStateChanged;
+            }
+        }
+
+        private void Update()
+        {
+            if (!isSpectating) return;
+
+            // Tab 키로 다음 관전 대상 전환
+            if (Input.GetKeyDown(nextTargetKey))
+            {
+                CycleToNextTarget();
+            }
+        }
+
+        private void HandleDeathStateChanged(bool dead)
+        {
+            if (dead)
+            {
+                StartSpectating();
+            }
+            else
+            {
+                StopSpectating();
+            }
+        }
+
+        /// <summary>
+        /// 관전 모드 시작
+        /// </summary>
+        private void StartSpectating()
+        {
+            // 살아있는 플레이어 목록 갱신
+            RefreshAlivePlayers();
+
+            if (alivePlayers.Count == 0)
+            {
+                // 관전할 플레이어가 없음 (게임 오버)
+                Debug.Log("[PlayerSpectator] No alive players to spectate");
+                return;
+            }
+
+            isSpectating = true;
+            currentSpectateIndex = 0;
+
+            // 첫 번째 살아있는 플레이어 관전
+            SetSpectateTarget(alivePlayers[currentSpectateIndex]);
+
+            OnSpectateModeChanged?.Invoke(true);
+
+            Debug.Log($"[PlayerSpectator] Started spectating. {alivePlayers.Count} players alive.");
+        }
+
+        /// <summary>
+        /// 관전 모드 종료
+        /// </summary>
+        private void StopSpectating()
+        {
+            isSpectating = false;
+            alivePlayers.Clear();
+            currentSpectateIndex = 0;
+
+            // 원래 플레이어로 카메라 복귀
+            if (playerCamera != null && networkController != null)
+            {
+                playerCamera.ResetToPlayer(networkController.transform);
+            }
+
+            OnSpectateModeChanged?.Invoke(false);
+
+            Debug.Log("[PlayerSpectator] Stopped spectating");
+        }
+
+        /// <summary>
+        /// 살아있는 플레이어 목록 갱신
+        /// </summary>
+        private void RefreshAlivePlayers()
+        {
+            alivePlayers.Clear();
+
+            var allPlayers = FindObjectsByType<PlayerNetworkController>(FindObjectsSortMode.None);
+            foreach (var player in allPlayers)
+            {
+                // 자신이 아니고, 살아있는 플레이어만 추가
+                if (player != networkController && !player.IsDead)
+                {
+                    alivePlayers.Add(player);
+                }
+            }
+        }
+
+        /// <summary>
+        /// 다음 관전 대상으로 전환
+        /// </summary>
+        private void CycleToNextTarget()
+        {
+            if (alivePlayers.Count == 0) return;
+
+            // 목록 갱신 (중간에 사망했을 수 있음)
+            RefreshAlivePlayers();
+
+            if (alivePlayers.Count == 0)
+            {
+                Debug.Log("[PlayerSpectator] No more alive players");
+                return;
+            }
+
+            currentSpectateIndex = (currentSpectateIndex + 1) % alivePlayers.Count;
+            SetSpectateTarget(alivePlayers[currentSpectateIndex]);
+        }
+
+        /// <summary>
+        /// 관전 대상 설정
+        /// </summary>
+        private void SetSpectateTarget(PlayerNetworkController target)
+        {
+            if (target == null || playerCamera == null) return;
+
+            playerCamera.SetTarget(target.transform);
+            OnSpectateTargetChanged?.Invoke(target);
+
+            Debug.Log($"[PlayerSpectator] Now spectating: Player {target.OwnerClientId}");
+        }
+
+        /// <summary>
+        /// 현재 관전 대상 이름 반환 (UI용)
+        /// </summary>
+        public string GetCurrentTargetName()
+        {
+            var target = CurrentTarget;
+            if (target == null) return "None";
+            return $"Player {target.OwnerClientId}";
+        }
+    }
+}