fix: 欢迎页语言切换器无效 #448

修复bootstrapLocale函数race condition问题，当用户通过localStorage手动选择语言时，尊重用户选择，不覆盖现有设置。

- 修改文件: apps/web/src/hooks/use-locale.tsx
- 新增逻辑: 在bootstrap过程中检查localStorage中的用户手动选择
- 修复问题: 欢迎页语言切换器无法改变UI语言的问题

Author: wcs04

apps/web/src/hooks/use-locale.tsx

@@ -114,10 +114,24 @@ async function bootstrapLocale(
   // flight, their selection is the source of truth — don't overwrite it.
   // Issue #759: on Windows zh-CN systems, the bootstrap was reverting a
   // user-selected English back to Chinese on the welcome screen.
+  // Issue #448: the welcome page language switcher does not change UI language
+  // because the bootstrap was overwriting the user's selection.
   if (userInteractedRef.current) {
     return;
   }
 
+  // If the user has manually selected a language via localStorage, use that
+  // as the source of truth and don't overwrite it with the server value.
+  try {
+    const manualSelection = localStorage.getItem(STORAGE_KEY);
+    if (manualSelection === "en" || manualSelection === "zh") {
+      // User has manually selected a language, respect their choice
+      return;
+    }
+  } catch {
+    /* ignore */
+  }
+
   if (storedLocale === "en" || storedLocale === "zh-CN") {
     const nextLocale = storedLocale === "zh-CN" ? "zh" : "en";
     await i18n.changeLanguage(nextLocale);