feat: tail interpolates like head (mirrored with ease-in)

Tail now uses the same approach as head: interpolated in the body path
from its previous position, with ease-in (mirror of head's ease-out).
Ghost circle removed — no longer needed since tail is naturally smooth.
Added EaseInCubic to AnimationHelper. InterpolatePosition now uses
string easing mode instead of bool.

Snake.Avalonia/Views/AnimationHelper.cs

@@ -26,7 +26,16 @@ public static class AnimationHelper
     }
 
     /// <summary>
-    /// Interpolates between two positions with given t value.
+    /// Ease-in cubic — mirror of EaseOutCubic, for tail interpolation.
+    /// </summary>
+    public static double EaseInCubic(double t)
+    {
+        t = Math.Clamp(t, 0.0, 1.0);
+        return t * t * t;
+    }
+
+    /// <summary>
+    /// Interpolates between two positions with given t value and easing mode.
     /// Returns the visual position for rendering.
     /// </summary>
     public static (double X, double Y) InterpolatePosition(
@@ -34,9 +43,14 @@ public static class AnimationHelper
         Position to,
         double t,
         double cellSize,
-        bool useEasing = false)
+        string easing = "linear")
     {
-        var eased = useEasing ? EaseOutCubic(t) : t;
+        var eased = easing switch
+        {
+            "easeOut" => EaseOutCubic(t),
+            "easeIn" => EaseInCubic(t),
+            _ => t
+        };
         var x = from.X + (to.X - from.X) * eased;
         var y = from.Y + (to.Y - from.Y) * eased;
         return (x * cellSize + cellSize * 0.5, y * cellSize + cellSize * 0.5);

Snake.Avalonia/Views/SnakeRenderer.cs

@@ -172,28 +172,6 @@ public sealed class SnakeRenderer : Control
             context.DrawGeometry(null, innerPen, bodyGeometry);
         }
 
-        // === Fading ghost circle at old tail position ===
-        // Creates the illusion of smooth tail movement without affecting
-        // the body path geometry (which stays grid-snapped with sharp corners).
-        if (count >= 2 && PreviousSegments != null && PreviousSegments.Count > 0)
-        {
-            var opacity = 0.4 * (1.0 - t);
-            if (opacity > 0)
-            {
-                var oldTailPos = PreviousSegments[PreviousSegments.Count - 1];
-                var currentTailPos = segmentsList[count - 1];
-
-                var (ghostX, ghostY) = AnimationHelper.InterpolatePosition(
-                    oldTailPos, currentTailPos, t, CellSize, useEasing: false);
-
-                context.DrawEllipse(
-                    new SolidColorBrush(SnakeBodyBrush.Color, opacity),
-                    null,
-                    new Point(ghostX, ghostY),
-                    CellSize * 0.35, CellSize * 0.35);
-            }
-        }
-
         // Draw head
         DrawHead(context, t);
 
@@ -379,17 +357,22 @@ public sealed class SnakeRenderer : Control
 
     private (double X, double Y) GetVisualPosition(Position pos, int segmentIndex, double t)
     {
-        // Head (index 0): interpolated with easing for smooth movement
+        if (Segments == null)
-        if (segmentIndex == 0)
+            return (pos.X * CellSize + CellSize * 0.5, pos.Y * CellSize + CellSize * 0.5);
-        {
+
+        var isHead = segmentIndex == 0;
+        var isTail = Segments.Count > 1 && segmentIndex == Segments.Count - 1;
+
+        // Head and tail interpolate smoothly; middle segments stay grid-snapped
+        if (!isHead && !isTail)
+            return (pos.X * CellSize + CellSize * 0.5, pos.Y * CellSize + CellSize * 0.5);
+
         var from = PreviousSegments != null && PreviousSegments.Count > 0
-                ? AnimationHelper.GetPreviousPosition(0, Segments!, PreviousSegments, SnakeDirection)
+            ? AnimationHelper.GetPreviousPosition(segmentIndex, Segments, PreviousSegments, SnakeDirection)
             : pos;
 
-            return AnimationHelper.InterpolatePosition(from, pos, t, CellSize, useEasing: true);
+        // Head: ease-out forward. Tail: ease-in backward (mirrored).
-        }
+        var easingMode = isHead ? "easeOut" : "easeIn";
-
+        return AnimationHelper.InterpolatePosition(from, pos, t, CellSize, easing: easingMode);
-        // All other segments (body and tail): grid-snapped for sharp corners
-        return (pos.X * CellSize + CellSize * 0.5, pos.Y * CellSize + CellSize * 0.5);
     }
 }