fix(mobile-app): 为每个火柴人跑道添加独立终点旗帜

- 移除单一的共享终点旗帜
- 为每个跑道生成独立的红旗，与火柴人垂直位置对齐

🤖 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

@@ -171,6 +171,10 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
     final trackCount = sortedRankings.length;
     final raceTrackHeight = (trackCount * _minTrackHeight).clamp(160.0, double.infinity);
 
+    // 计算每个跑道的高度和位置
+    final usableHeight = raceTrackHeight - 40;
+    final trackHeight = usableHeight / trackCount;
+
     return SizedBox(
       height: raceTrackHeight,
       child: Stack(
@@ -184,31 +188,19 @@ class _StickmanRaceWidgetState extends State<StickmanRaceWidget>
             ),
           ),
 
-          // 终点红旗
-          Positioned(
-            right: 8,
-            top: 0,
-            bottom: 40,
-            child: Column(
-              mainAxisAlignment: MainAxisAlignment.center,
-              children: const [
-                Icon(
-                  Icons.flag,
-                  color: Colors.red,
-                  size: 32,
-                ),
-                SizedBox(height: 4),
-                Text(
-                  '终点',
-                  style: TextStyle(
-                    fontSize: 10,
-                    fontFamily: 'Inter',
-                    color: Color(0xFF8B5A2B),
-                  ),
-                ),
-              ],
-            ),
-          ),
+          // 每个跑道的终点红旗
+          ...List.generate(trackCount, (index) {
+            final verticalPosition = index * trackHeight + 10 + trackHeight / 2 - 16;
+            return Positioned(
+              right: 8,
+              top: verticalPosition,
+              child: const Icon(
+                Icons.flag,
+                color: Colors.red,
+                size: 24,
+              ),
+            );
+          }),
 
           // 火柴人们
           ...sortedRankings.asMap().entries.map((entry) {