feat: define path smoothing contracts

ClumsyPilot/ParkrobTrajplanner/PathSmoothing/Contracts/LocalCubicBezierOptions.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace MultiWheelC.TrajectoryPlanning.PathSmoothing;
+
+/// <summary>局部三次 Bézier 平滑参数。</summary>
+public sealed class LocalCubicBezierOptions
+{
+    /// <summary>判定为明显转角的最小航向变化，单位 rad。</summary>
+    public double CornerHeadingThresholdRadians { get; set; } = Math.PI / 18d;
+
+    /// <summary>单个局部平滑窗口的最大弧长，单位 m。</summary>
+    public double MaximumWindowLengthMeters { get; set; } = 0.60d;
+
+    /// <summary>控制柄相对于窗口局部弦长的比例。</summary>
+    public double HandleLengthRatio { get; set; } = 1d / 3d;
+}