feat: Improve path preview visualization in UnifiedAGVCanvas

Enhanced path drawing with better visibility:

1. Arrow improvements:
   - Changed from line-based arrows to filled triangle shapes
   - Increased arrow size by 1.5x for better visibility
   - Added polygon fill with outline for clearer identification

2. Path line improvements:
   - Added 50% transparency to purple path color (Alpha: 128)
   - Increased line thickness by 2x (from 4 to 8 pixels)
   - Improved visual contrast and clarity

3. Bidirectional path detection:
   - Detect routes that traverse the same segment multiple times
   - Display bidirectional paths with higher opacity (darker color, Alpha: 200)
   - Visual distinction helps identify round-trip routes

Changes in UnifiedAGVCanvas.Events.cs:
- Modified DrawDirectionArrow() to use FillPolygon instead of DrawLine
- Enhanced DrawPath() with transparency, thickness, and bidirectional detection
- Added System.Collections.Generic using statement

Result: Much better visual identification of calculated paths in HMI

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Cs_HMI/AGVLogic/AGVNavigationCore/Controls/UnifiedAGVCanvas.Events.cs

@@ -2,6 +2,7 @@ using AGVNavigationCore.Models;
 using AGVNavigationCore.PathFinding;
 using AGVNavigationCore.PathFinding.Core;
 using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.Drawing.Drawing2D;
 using System.Linq;
@@ -153,28 +154,42 @@ namespace AGVNavigationCore.Controls
 
         private void DrawDirectionArrow(Graphics g, Point point, double angle, AgvDirection direction)
         {
-            var arrowSize = CONNECTION_ARROW_SIZE;
+            var arrowSize = CONNECTION_ARROW_SIZE * 1.5; // 화살표 크기 증가
             var arrowAngle = Math.PI / 6; // 30도
 
             var cos = Math.Cos(angle);
             var sin = Math.Sin(angle);
 
+            // 화살표 끝점 (방향)
+            var arrowTipPoint = new Point(
+                (int)(point.X + arrowSize * Math.Cos(angle)),
+                (int)(point.Y + arrowSize * Math.Sin(angle))
+            );
+
+            // 화살표 좌측 점
             var arrowPoint1 = new Point(
                 (int)(point.X - arrowSize * Math.Cos(angle - arrowAngle)),
                 (int)(point.Y - arrowSize * Math.Sin(angle - arrowAngle))
             );
 
+            // 화살표 우측 점
             var arrowPoint2 = new Point(
                 (int)(point.X - arrowSize * Math.Cos(angle + arrowAngle)),
                 (int)(point.Y - arrowSize * Math.Sin(angle + arrowAngle))
             );
 
             var arrowColor = direction == AgvDirection.Forward ? Color.Blue : Color.Red;
-            var arrowPen = new Pen(arrowColor, 2);
+            var arrowBrush = new SolidBrush(arrowColor);
 
-            g.DrawLine(arrowPen, point, arrowPoint1);
-            g.DrawLine(arrowPen, point, arrowPoint2);
+            // 삼각형으로 화살표 그리기 (내부 채움)
+            var trianglePoints = new Point[] { arrowTipPoint, arrowPoint1, arrowPoint2 };
+            g.FillPolygon(arrowBrush, trianglePoints);
 
+            // 윤곽선 그리기
+            var arrowPen = new Pen(arrowColor, 1.5f);
+            g.DrawPolygon(arrowPen, trianglePoints);
+
+            arrowBrush.Dispose();
             arrowPen.Dispose();
         }
 
@@ -204,20 +219,55 @@ namespace AGVNavigationCore.Controls
         {
             if (path?.Path == null || path.Path.Count < 2) return;
 
-            var pathPen = new Pen(color, 4) { DashStyle = DashStyle.Dash };
+            // 현재 선택된 경로인 경우 보라색 + 투명도 50% + 선 두께 2배
+            Color lineColor = color;
+            float lineThickness = 4;
+
+            if (color == Color.Purple)
+            {
+                // 투명도 50% (Alpha = 128 / 255)
+                lineColor = Color.FromArgb(128, color.R, color.G, color.B);
+                lineThickness = 8; // 2배 증가
+            }
+
+            var pathPen = new Pen(lineColor, lineThickness) { DashStyle = DashStyle.Dash };
+
+            // 왕복 경로 감지: 방문한 노드 추적
+            var visitedSegments = new Dictionary<string, int>();
 
             for (int i = 0; i < path.Path.Count - 1; i++)
             {
                 var currentNodeId = path.Path[i];
                 var nextNodeId = path.Path[i + 1];
 
+                // 왕복 구간 키 생성 (양방향 모두 같은 키)
+                var segmentKey = string.Compare(currentNodeId, nextNodeId) < 0
+                    ? $"{currentNodeId}_{nextNodeId}"
+                    : $"{nextNodeId}_{currentNodeId}";
+
+                if (!visitedSegments.ContainsKey(segmentKey))
+                    visitedSegments[segmentKey] = 0;
+                visitedSegments[segmentKey]++;
+
                 var currentNode = _nodes?.FirstOrDefault(n => n.NodeId == currentNodeId);
                 var nextNode = _nodes?.FirstOrDefault(n => n.NodeId == nextNodeId);
 
                 if (currentNode != null && nextNode != null)
                 {
-                    // 경로 선 그리기
+                    // 왕복 경로면 더 진한 색상으로 표시
+                    if (visitedSegments[segmentKey] > 1 && color == Color.Purple)
+                    {
+                        // 왕복 경로는 투명도를 낮춤 (더 진하게)
+                        var darkPathColor = Color.FromArgb(200, color.R, color.G, color.B);
+                        var darkPathPen = new Pen(darkPathColor, lineThickness) { DashStyle = DashStyle.Dash };
+                        g.DrawLine(darkPathPen, currentNode.Position, nextNode.Position);
+                        darkPathPen.Dispose();
+                    }
+                    else
+                    {
+                        // 일반 경로 선 그리기
                         g.DrawLine(pathPen, currentNode.Position, nextNode.Position);
+                    }
 
                     // 경로 방향 표시 (계산된 경로의 경우에만 방향 화살표 표시)
                     var midPoint = new Point(