fix(mobile): 修复火柴人组件布局错误，避免嵌套Stack

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/authorization/presentation/widgets/stickman_race_widget.dart

@@ -188,9 +188,8 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
         builder: (context, constraints) {
           final containerWidth = constraints.maxWidth;
 
-          return Stack(
-            clipBehavior: Clip.none,
-            children: [
+          // 收集所有 Positioned widgets
+          final List<Widget> children = [
             // 背景赛道线
             Positioned.fill(
               child: CustomPaint(
@@ -199,11 +198,12 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
                 ),
               ),
             ),
+          ];
 
-              // 每个跑道的终点红旗
-              ...List.generate(trackCount, (index) {
+          // 添加每个跑道的终点红旗
+          for (int index = 0; index < trackCount; index++) {
             final verticalPosition = index * trackHeight + 10 + trackHeight / 2 - 16;
-                return Positioned(
+            children.add(Positioned(
               right: 8,
               top: verticalPosition,
               child: const Icon(
@@ -211,24 +211,32 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
                 color: Colors.red,
                 size: 24,
               ),
-                );
-              }),
+            ));
+          }
 
-              // 火柴人们
-              ...sortedRankings.asMap().entries.map((entry) {
-                final index = entry.key;
-                final data = entry.value;
-                return _buildStickman(data, index, sortedRankings.length, raceTrackHeight, containerWidth);
-              }),
-            ],
+          // 添加火柴人们（昵称和火柴人分开添加）
+          for (int index = 0; index < sortedRankings.length; index++) {
+            final data = sortedRankings[index];
+            final widgets = _buildStickmanWidgets(data, index, sortedRankings.length, raceTrackHeight, containerWidth);
+            children.addAll(widgets);
+          }
+
+          return AnimatedBuilder(
+            animation: _bounceController,
+            builder: (context, child) {
+              return Stack(
+                clipBehavior: Clip.none,
+                children: children,
+              );
+            },
           );
         },
       ),
     );
   }
 
-  /// 构建单个火柴人
-  Widget _buildStickman(StickmanRankingData data, int rank, int total, double raceTrackHeight, double containerWidth) {
+  /// 构建单个火柴人的所有 Positioned widgets
+  List<Widget> _buildStickmanWidgets(StickmanRankingData data, int rank, int total, double raceTrackHeight, double containerWidth) {
     // 进度 (0.0 - 1.0)
     final progress = data.progress;
 
@@ -237,22 +245,16 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
     final trackHeight = usableHeight / total;
     final verticalPosition = rank * trackHeight + 10;
 
-    // 火柴人列宽度约50（数量标签maxWidth:60，但实际更窄）
-    // 红旗: right=8, width=24, 所以红旗左边 = containerWidth - 32
-    // 火柴人停在红旗左边时: stickmanLeft + 50 = containerWidth - 32
-    // 所以 endX = containerWidth - 82
+    // 简单计算:
+    // 起点 = 70 (昵称区域右边)
+    // 终点 = 红旗左边位置 - 火柴人宽度 = (containerWidth - 32) - 50 = containerWidth - 82
     const double startX = 70.0;
     final double endX = containerWidth - 82.0;
     final double stickmanLeft = startX + (endX - startX) * progress;
 
-    return AnimatedBuilder(
-      animation: _bounceController,
-      builder: (context, child) {
     final bounce = _bounceController.value * 3;
 
-        return Stack(
-          clipBehavior: Clip.none,
-          children: [
+    return [
       // 昵称标签 - 固定在左边
       Positioned(
         left: 0,
@@ -327,10 +329,7 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
           ],
         ),
       ),
-          ],
-        );
-      },
-    );
+    ];
   }
 
   /// 构建进度条