feat: Implement Room Streaming System

- Add RoomStreamingManager to manage room loading and unloading based on player proximity.
- Create StreamingBudgetConfigSO for memory and performance budgeting of the streaming system.
- Introduce TransitionDirector to handle seamless and atmospheric fade transitions between rooms.
- Develop WorldGraph to represent room connectivity and facilitate neighbor queries and distance calculations.
- Implement RoomNode and RoomEdge classes to structure room data and connections.

Assets/_Game/Scripts/Enemies/AI/BD_MaintainCombatDistance.cs

@@ -0,0 +1,96 @@
+#if GRAPH_DESIGNER
+using Opsive.BehaviorDesigner.Runtime.Tasks;
+using Opsive.BehaviorDesigner.Runtime.Tasks.Actions;
+using UnityEngine;
+
+namespace BaseGames.Enemies.AI
+{
+    /// <summary>
+    /// BD Action：战斗站位控制。
+    /// 在 [m_PreferredMinDist, m_PreferredMaxDist] 范围内保持与玩家的水平距离：
+    ///   - 距离过近 → 后退
+    ///   - 距离过远 → 靠近
+    ///   - 在范围内 → 停止移动，持续朝向玩家
+    /// 始终返回 Running，上层 BT 通过 Abort 或条件终止该 Task。
+    /// </summary>
+    [TaskName("Maintain Combat Distance")]
+    [TaskCategory("BaseGames/Enemy/Combat")]
+    [TaskDescription("在战斗中维持与目标的理想距离范围")]
+    public class BD_MaintainCombatDistance : Action
+    {
+        [Tooltip("期望最小距离（m）；小于此值开始后退")]
+        [SerializeField] private float m_PreferredMinDist = 2f;
+
+        [Tooltip("期望最大距离（m）；大于此值开始靠近")]
+        [SerializeField] private float m_PreferredMaxDist = 4f;
+
+        [Tooltip("后退速度（m/s），默认使用 WalkSpeed")]
+        [SerializeField] private float m_BackpedaleSpeed = 0f;
+
+        [Tooltip("每帧重新规划路径的阈值（m）；玩家移动超过此距离才重规划，降低频率")]
+        [SerializeField] private float m_ReplanThreshold = 0.5f;
+
+        private EnemyBase _enemy;
+        private Vector2   _lastPlayerPos;
+        private float     _sqrMin;
+        private float     _sqrMax;
+
+        public override void OnAwake() => _enemy = GetComponent<EnemyBase>();
+
+        public override void OnStart()
+        {
+            _sqrMin        = m_PreferredMinDist * m_PreferredMinDist;
+            _sqrMax        = m_PreferredMaxDist * m_PreferredMaxDist;
+            _lastPlayerPos = Vector2.positiveInfinity;
+        }
+
+        public override TaskStatus OnUpdate()
+        {
+            if (_enemy == null || _enemy.PlayerTransform == null)
+                return TaskStatus.Failure;
+
+            if (_enemy.Stats == null)
+                return TaskStatus.Failure;
+
+            _enemy.FacePlayer();
+
+            float sqrDist = _enemy.Stats.SqrDistanceToPlayer;
+
+            if (sqrDist < _sqrMin)
+            {
+                // 距离过近 → 后退（向远离玩家方向移动）
+                _enemy.Nav?.StopNavigation();
+                Vector2 toPlayer  = ((Vector2)_enemy.PlayerTransform.position - (Vector2)_enemy.transform.position).normalized;
+                float   backDir   = -Mathf.Sign(toPlayer.x);
+                float   speed     = m_BackpedaleSpeed > 0f ? m_BackpedaleSpeed : _enemy.Stats.WalkSpeed;
+                _enemy.Movement?.MoveWithSpeed(backDir, speed);
+            }
+            else if (sqrDist > _sqrMax)
+            {
+                // 距离过远 → 靠近
+                Vector2 playerPos = _enemy.PlayerTransform.position;
+                float   moved     = ((Vector2)playerPos - _lastPlayerPos).sqrMagnitude;
+                if (moved > m_ReplanThreshold * m_ReplanThreshold)
+                {
+                    _lastPlayerPos = playerPos;
+                    _enemy.MoveTo(playerPos);
+                }
+            }
+            else
+            {
+                // 在最优范围内 → 停止导航，原地保持朝向
+                _enemy.Nav?.StopNavigation();
+                _enemy.Movement?.StopHorizontal();
+            }
+
+            return TaskStatus.Running;
+        }
+
+        public override void OnEnd()
+        {
+            _enemy?.Movement?.StopHorizontal();
+            _enemy?.Nav?.StopNavigation();
+        }
+    }
+}
+#endif