UI: Unify trader colors between Leaderboard and Performance Chart

Problem:
- Leaderboard used ai_model-based colors (qwen=purple, other=blue)
- Performance Comparison used index-based colors (10 color pool)
- This caused color mismatch between the two components
- Same trader showed different colors in different sections

Solution:
- Create shared color utility (utils/traderColors.ts)
- Define single color pool with 10 distinct colors
- Implement unified getTraderColor function based on trader index
- Update both ComparisonChart and CompetitionPage to use shared utility

Changes:
- New file: web/src/utils/traderColors.ts (shared color logic)
- Updated: ComparisonChart.tsx (use shared utility)
- Updated: CompetitionPage.tsx (use shared utility in Leaderboard
  and Head-to-Head sections)

Now traders consistently display the same color across all UI sections.

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

Co-Authored-By: tinkle-community <tinklefund@gmail.com>

web/src/utils/traderColors.ts

@@ -0,0 +1,31 @@
+// Trader颜色配置 - 统一的颜色分配逻辑
+// 用于 ComparisonChart 和 Leaderboard，确保颜色一致性
+
+export const TRADER_COLORS = [
+  '#60a5fa', // blue-400
+  '#c084fc', // purple-400
+  '#34d399', // emerald-400
+  '#fb923c', // orange-400
+  '#f472b6', // pink-400
+  '#fbbf24', // amber-400
+  '#38bdf8', // sky-400
+  '#a78bfa', // violet-400
+  '#4ade80', // green-400
+  '#fb7185', // rose-400
+];
+
+/**
+ * 根据trader的索引位置获取颜色
+ * @param traders - trader列表
+ * @param traderId - 当前trader的ID
+ * @returns 对应的颜色值
+ */
+export function getTraderColor(
+  traders: Array<{ trader_id: string }>,
+  traderId: string
+): string {
+  const traderIndex = traders.findIndex((t) => t.trader_id === traderId);
+  if (traderIndex === -1) return TRADER_COLORS[0]; // 默认返回第一个颜色
+  // 如果超出颜色池大小，循环使用
+  return TRADER_COLORS[traderIndex % TRADER_COLORS.length];
+}