fix(TradingSimulation): 修复 React Hooks 调用顺序错误

提取 JSX 中直接调用的 useColorModeValue 到组件顶部，避免 Hooks 顺序不一致。

修改内容：
- 在第 95 行添加 contentTextColor 常量
- 替换第 350 行 Heading 中的内联 Hook 调用
- 替换第 361 行 Text 中的内联 Hook 调用

修复警告：React has detected a change in the order of Hooks called by TradingSimulation

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

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

src/views/TradingSimulation/index.js

@@ -92,6 +92,7 @@ export default function TradingSimulation() {
   const xAxisLabelColor = useColorModeValue('#718096', '#A0AEC0');
   const yAxisLabelColor = useColorModeValue('#718096', '#A0AEC0');
   const gridBorderColor = useColorModeValue('#E2E8F0', '#4A5568');
+  const contentTextColor = useColorModeValue('gray.700', 'white');
 
   // ========== 2. 所有 useEffect 也必须在条件返回之前 ==========
   useEffect(() => {
@@ -346,7 +347,7 @@ export default function TradingSimulation() {
             <VStack spacing={6} align="stretch">
               {/* 账户概览统计 */}
               <Box>
-                <Heading size="lg" mb={4} color={useColorModeValue('gray.700', 'white')}>
+                <Heading size="lg" mb={4} color={contentTextColor}>
                   📊 账户统计分析
                 </Heading>
                 <AccountOverview account={account} tradingEvents={tradingEvents} />
@@ -357,7 +358,7 @@ export default function TradingSimulation() {
                 <Card>
                   <CardHeader>
                     <HStack justify="space-between">
-                      <Text fontSize="lg" fontWeight="bold" color={useColorModeValue('gray.700', 'white')}>
+                      <Text fontSize="lg" fontWeight="bold" color={contentTextColor}>
                         📈 资产走势分析
                       </Text>
                       <Badge colorScheme="purple" variant="outline">