fix: 自由路径保持物体原始姿态，起点不做自动旋转调整

真实物体(YUp)的自由路径自动对齐路径方向的旋转在宿主/几何姿态
解析上容易出错（对齐了错误前向、侧滚90°）。按用户要求，自由路径
改为保持物体原始姿态：
- MoveObjectToPathStart：自由路径纯平移（ApplyTrackedTranslationOnly），
  不应用任何自动旋转
- ShouldPreservePathRotationForFrames：对 Free 始终返回 true，帧锁定
  起点姿态，物体沿路径平移而保持朝向
- 移除废弃的 TryCreateFreePathRotationForFrame/AtStart（平面自动旋转）
257 单测全过。

src/Core/Animation/PathAnimationManager.cs

@@ -955,16 +955,13 @@ namespace NavisworksTransport.Core.Animation
                         _hasGroundRealObjectBasePose = false;
                     }
                 }
-                else if (_route.PathType == PathType.Free &&
-                    TryCreateFreePathRotationAtStart(out var freeStartRotation))
-                {
-                    ApplyFullPoseUpdate(startPosition, freeStartRotation);
-                    LogManager.Debug("[移动到起点] 自由路径已应用完整三维姿态（切线前向 + 世界up正交化）");
-                }
                 else if (_route.PathType == PathType.Free)
                 {
-                    LogManager.Error("[移动到起点] 自由路径未能生成完整三维姿态，已禁止退回旧 yaw 链路");
-                    return false;
+                    // 自由路径：保持物体原始姿态，仅平移到起点（不做任何自动旋转调整）
+                    ApplyTrackedTranslationOnly(startPosition);
+                    SyncTrackedRotationToDisplayedPose(CurrentControlledObject ?? _animatedObject);
+                    _hasGroundRealObjectBasePose = false;
+                    LogManager.Debug("[移动到起点] 自由路径已保持原始姿态纯平移到起点");
                 }
                 else if (_route.PathType == PathType.Ground || _route.PathType == PathType.Hoisting)
                 {
@@ -1508,12 +1505,6 @@ namespace NavisworksTransport.Core.Animation
                         frame.Rotation = railRotation;
                         frame.HasCustomRotation = true;
                     }
-                    else if (_route.PathType == PathType.Free &&
-                             TryCreateFreePathRotationForFrame(previousFramePoint, framePosition, nextFramePoint, out var freeRotation))
-                    {
-                        frame.Rotation = freeRotation;
-                        frame.HasCustomRotation = true;
-                    }
                     else if ((_route.PathType == PathType.Ground || _route.PathType == PathType.Hoisting) &&
                              !_route.IsTwoPointVertical &&
                              TryCreatePlanarPathRotationForFrame(previousFramePoint, framePosition, nextFramePoint, out var planarRotation))
@@ -4030,7 +4021,18 @@ namespace NavisworksTransport.Core.Animation
             ObjectStartPlacementMode placementMode,
             bool hasPreservedRotation)
         {
-            if (!hasPreservedRotation || placementMode != ObjectStartPlacementMode.PreserveInitialPose)
+            if (!hasPreservedRotation)
+            {
+                return false;
+            }
+
+            // 自由路径：保持物体原始姿态，不自动对齐路径方向（用户通过"调整物体"控制朝向）
+            if (pathType == PathType.Free)
+            {
+                return true;
+            }
+
+            if (placementMode != ObjectStartPlacementMode.PreserveInitialPose)
             {
                 return false;
             }
@@ -4937,61 +4939,6 @@ namespace NavisworksTransport.Core.Animation
             return true;
         }
 
-        /// <summary>
-        /// 自由路径姿态（平面）：像地面路径一样，物体转向前进方向的水平投影，
-        /// 但只绕垂直轴（up 轴）旋转（yaw），不绕前进轴滚动。
-        /// 复用 CanonicalPlanarPoseBuilder（forward=路径水平投影，up=世界up）。
-        /// </summary>
-        private bool TryCreateFreePathRotationForFrame(Point3D previousPoint, Point3D currentPoint, Point3D nextPoint, out Rotation3D rotation)
-        {
-            rotation = Rotation3D.Identity;
-
-            var adapter = CoordinateSystemManager.Instance.CreateHostAdapter();
-            var convention = GetCurrentModelAxisConvention();
-
-            Vector3 canonicalPrevious = ToNumerics(adapter.ToCanonicalPoint(previousPoint));
-            Vector3 canonicalCurrent = ToNumerics(adapter.ToCanonicalPoint(currentPoint));
-            Vector3 canonicalNext = ToNumerics(adapter.ToCanonicalPoint(nextPoint));
-
-            Vector3 canonicalForward = canonicalNext - canonicalPrevious;
-            if (canonicalForward.LengthSquared() < 1e-6f)
-            {
-                canonicalForward = canonicalNext - canonicalCurrent;
-            }
-
-            if (!CanonicalPlanarPoseBuilder.TryCreateQuaternionFromForward(
-                canonicalForward,
-                HostCoordinateAdapter.CanonicalUpVector3,
-                convention,
-                _objectRotationCorrection,
-                out var canonicalRotation))
-            {
-                return false;
-            }
-
-            rotation = adapter.FromCanonicalRotation(canonicalRotation);
-            return true;
-        }
-
-        /// <summary>
-        /// 自由路径起点姿态：以首段方向水平投影为前向，只绕垂直轴旋转（yaw）。
-        /// </summary>
-        private bool TryCreateFreePathRotationAtStart(out Rotation3D rotation)
-        {
-            rotation = Rotation3D.Identity;
-
-            if (_pathPoints == null || _pathPoints.Count < 2)
-            {
-                return false;
-            }
-
-            return TryCreateFreePathRotationForFrame(
-                _pathPoints[0],
-                _pathPoints[0],
-                _pathPoints[1],
-                out rotation);
-        }
-
         private bool TryCreateRailPathRotation(
             Point3D previousPoint,
             Point3D currentPoint,