fix(mobile): 简化火柴人位置计算逻辑

使用简单直接的比例计算：
- 起点 = 昵称区域右边 (70px)
- 终点 = 红旗左边 (containerWidth - 62px)
- 火柴人位置 = 起点 + (终点 - 起点) * 进度

🤖 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

@@ -183,7 +183,12 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
 
     return SizedBox(
       height: raceTrackHeight,
-      child: Stack(
+      child: LayoutBuilder(
+        builder: (context, constraints) {
+          final containerWidth = constraints.maxWidth;
+
+          return Stack(
+            clipBehavior: Clip.none,
             children: [
               // 背景赛道线
               Positioned.fill(
@@ -212,59 +217,47 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
               ...sortedRankings.asMap().entries.map((entry) {
                 final index = entry.key;
                 final data = entry.value;
-            return _buildStickman(data, index, sortedRankings.length, raceTrackHeight);
+                return _buildStickman(data, index, sortedRankings.length, raceTrackHeight, containerWidth);
               }),
             ],
+          );
+        },
       ),
     );
   }
 
   /// 构建单个火柴人
-  Widget _buildStickman(StickmanRankingData data, int rank, int total, double raceTrackHeight) {
-    // 计算水平位置 (根据进度)
-    final horizontalProgress = data.progress;
+  Widget _buildStickman(StickmanRankingData data, int rank, int total, double raceTrackHeight, double containerWidth) {
+    // 进度 (0.0 - 1.0)
+    final progress = data.progress;
 
     // 计算垂直位置 (不同排名在不同跑道)
-    // 预留顶部和底部空间
     final usableHeight = raceTrackHeight - 40;
     final trackHeight = usableHeight / total;
     final verticalPosition = rank * trackHeight + 10;
 
+    // 简单直接的计算：
+    // 起点：昵称区域右边 (70)
+    // 终点：红旗左边 (containerWidth - 8(红旗right) - 24(红旗宽) - 30(火柴人半宽))
+    // 火柴人中心位置 = 起点 + (终点 - 起点) * 进度
+    const double startX = 70.0;
+    final double endX = containerWidth - 62.0;
+    final double stickmanCenterX = startX + (endX - startX) * progress;
+
     return AnimatedBuilder(
       animation: _bounceController,
       builder: (context, child) {
-        // 添加上下弹跳效果
         final bounce = _bounceController.value * 3;
 
-        // 计算可用宽度，让火柴人在100%时正好到达红旗位置
-        final screenWidth = MediaQuery.of(context).size.width;
-        final containerWidth = screenWidth - 32 - 32; // 页面padding + 容器padding
-        final stickmanColumnWidth = 60.0; // 火柴人+数量标签列的宽度
-        final flagRightMargin = 8.0; // 红旗的right值
-        final flagWidth = 24.0; // 红旗图标宽度
-        final nicknameAreaWidth = 65.0; // 昵称区域宽度
-        final gap = 4.0; // 昵称和火柴人之间的最小间距
-
-        // 100%时火柴人列的右边缘应该对齐红旗左边缘
-        // 红旗左边位置 = containerWidth - flagRightMargin - flagWidth
-        // 火柴人列右边 = stickmanLeftPosition + stickmanColumnWidth
-        // 所以 100% 时: stickmanLeftPosition = containerWidth - flagRightMargin - flagWidth - stickmanColumnWidth
-        final endPosition = containerWidth - flagRightMargin - flagWidth - stickmanColumnWidth;
-        final startPosition = nicknameAreaWidth + gap;
-        final availableWidth = endPosition - startPosition;
-        final stickmanLeftPosition = startPosition + availableWidth * horizontalProgress;
-
-        return Positioned(
-          left: 0,
-          top: verticalPosition - bounce,
-          child: SizedBox(
-            width: containerWidth,
-            child: Row(
-              crossAxisAlignment: CrossAxisAlignment.start,
+        return Stack(
+          clipBehavior: Clip.none,
           children: [
-                // 昵称标签 - 固定在左边，与数量标签同一水平高度
-                SizedBox(
-                  width: nicknameAreaWidth,
+            // 昵称标签 - 固定在左边
+            Positioned(
+              left: 0,
+              top: verticalPosition + 15 - bounce,
+              child: SizedBox(
+                width: 65,
                 child: Container(
                   padding: const EdgeInsets.symmetric(horizontal: 4, vertical: 2),
                   decoration: BoxDecoration(
@@ -281,8 +274,7 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
                     style: TextStyle(
                       fontSize: 9,
                       fontFamily: 'Inter',
-                        fontWeight:
-                            data.isCurrentUser ? FontWeight.w600 : FontWeight.w400,
+                      fontWeight: data.isCurrentUser ? FontWeight.w600 : FontWeight.w400,
                       color: data.isCurrentUser
                           ? const Color(0xFFD4AF37)
                           : const Color(0xFF5D4037),
@@ -292,12 +284,12 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
                   ),
                 ),
               ),
-                // 间隔 + 火柴人位置
-                SizedBox(
-                  width: stickmanLeftPosition - nicknameAreaWidth,
             ),
             // 火柴人和数量标签
-                Column(
+            Positioned(
+              left: stickmanCenterX - 30,  // 火柴人宽度60的一半
+              top: verticalPosition - bounce,
+              child: Column(
                 mainAxisSize: MainAxisSize.min,
                 children: [
                   // 完成数量标签
@@ -333,9 +325,8 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
                   ),
                 ],
               ),
+            ),
           ],
-            ),
-          ),
         );
       },
     );