fix: 修复个股搜索下拉弹窗被遮挡的问题

Hero Section 的 overflow: hidden 会裁剪超出边界的搜索下拉框，
改为 overflow: visible 解决此问题。

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

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

src/views/StockOverview/index.js

@@ -583,7 +583,7 @@ const StockOverview = () => {
         position="relative"
         bgGradient={heroBg}
         color="white"
-        overflow="hidden"
+        overflow="visible"
         pt={{ base: 20, md: 24 }}
         pb={{ base: 16, md: 20 }}
         borderBottom={colorMode === 'dark' ? `2px solid ${goldColor}` : 'none'}