init: 初始化 AssetX 项目仓库

包含 webapp（Next.js 用户端）、webapp-back（Go 后端）、
antdesign（管理后台）、landingpage（营销落地页）、
数据库 SQL 和配置文件。

webapp/contexts/AppContext.tsx

@@ -0,0 +1,123 @@
+"use client";
+
+import { createContext, useContext, useState, useEffect, useMemo, useCallback, ReactNode } from "react";
+
+type Language = "zh" | "en";
+type Theme = "light" | "dark";
+
+const VALID_LANGUAGES: Language[] = ["zh", "en"];
+const VALID_THEMES: Theme[] = ["light", "dark"];
+
+function isValidLanguage(val: unknown): val is Language {
+  return typeof val === 'string' && VALID_LANGUAGES.includes(val as Language);
+}
+
+function isValidTheme(val: unknown): val is Theme {
+  return typeof val === 'string' && VALID_THEMES.includes(val as Theme);
+}
+
+interface AppContextType {
+  language: Language;
+  setLanguage: (lang: Language) => void;
+  theme: Theme;
+  setTheme: (theme: Theme) => void;
+  t: (key: string) => string;
+}
+
+const AppContext = createContext<AppContextType | undefined>(undefined);
+
+// 模块级翻译缓存
+const translationCache: Record<string, Record<string, unknown>> = {};
+
+function loadTranslations(lang: Language): Record<string, unknown> {
+  if (!translationCache[lang]) {
+    translationCache[lang] = require(`../locales/${lang}.json`);
+  }
+  return translationCache[lang];
+}
+
+export function AppProvider({ children }: { children: ReactNode }) {
+  const [language, setLanguageState] = useState<Language>("en");
+  const [theme, setThemeState] = useState<Theme>("light");
+  const [mounted, setMounted] = useState(false);
+
+  // SSR 守卫：仅 mounted 后读取 localStorage/matchMedia
+  useEffect(() => {
+    setMounted(true);
+    try {
+      const savedLanguage = localStorage.getItem("language");
+      if (isValidLanguage(savedLanguage)) {
+        setLanguageState(savedLanguage);
+      }
+      // 强制 light 主题
+      localStorage.setItem("theme", "light");
+    } catch {
+      // 隐私模式或 localStorage 不可用
+    }
+  }, []);
+
+  // Apply theme
+  useEffect(() => {
+    if (!mounted) return;
+    try {
+      localStorage.setItem("theme", theme);
+    } catch {
+      // 隐私模式兼容
+    }
+    if (theme === "dark") {
+      document.documentElement.classList.add("dark");
+    } else {
+      document.documentElement.classList.remove("dark");
+    }
+  }, [theme, mounted]);
+
+  // Save language preference
+  const setLanguage = useCallback((lang: Language) => {
+    setLanguageState(lang);
+    try {
+      localStorage.setItem("language", lang);
+    } catch {
+      // 隐私模式兼容
+    }
+  }, []);
+
+  const setTheme = useCallback((t: Theme) => {
+    setThemeState(t);
+  }, []);
+
+  // Translation function — 使用模块级缓存
+  const t = useCallback((key: string): string => {
+    const translations = loadTranslations(language);
+    const keys = key.split(".");
+    let value: unknown = translations;
+
+    for (const k of keys) {
+      if (typeof value === 'object' && value !== null) {
+        value = (value as Record<string, unknown>)[k];
+      } else {
+        return key;
+      }
+    }
+
+    return typeof value === 'string' ? value : key;
+  }, [language]);
+
+  const contextValue = useMemo(
+    () => ({ language, setLanguage, theme, setTheme, t }),
+    [language, setLanguage, theme, setTheme, t]
+  );
+
+  return (
+    <AppContext.Provider value={contextValue}>
+      {children}
+    </AppContext.Provider>
+  );
+}
+
+export function useApp() {
+  const context = useContext(AppContext);
+  if (!context) {
+    throw new Error("useApp must be used within AppProvider");
+  }
+  return context;
+}