Feature: Add multi-language support and UI improvements

- Add language context and translation system (Chinese/English)
- Enhance UI components with i18n support
- Update AILearning, EquityChart, and CompetitionPage
- Add language toggle in header
- Improve user experience with localized text

web/src/contexts/LanguageContext.tsx

@@ -0,0 +1,37 @@
+import { createContext, useContext, useState, ReactNode } from 'react';
+import type { Language } from '../i18n/translations';
+
+interface LanguageContextType {
+  language: Language;
+  setLanguage: (lang: Language) => void;
+}
+
+const LanguageContext = createContext<LanguageContextType | undefined>(undefined);
+
+export function LanguageProvider({ children }: { children: ReactNode }) {
+  // Initialize language from localStorage or default to English
+  const [language, setLanguage] = useState<Language>(() => {
+    const saved = localStorage.getItem('language');
+    return (saved === 'en' || saved === 'zh') ? saved : 'en';
+  });
+
+  // Save language to localStorage whenever it changes
+  const handleSetLanguage = (lang: Language) => {
+    setLanguage(lang);
+    localStorage.setItem('language', lang);
+  };
+
+  return (
+    <LanguageContext.Provider value={{ language, setLanguage: handleSetLanguage }}>
+      {children}
+    </LanguageContext.Provider>
+  );
+}
+
+export function useLanguage() {
+  const context = useContext(LanguageContext);
+  if (!context) {
+    throw new Error('useLanguage must be used within LanguageProvider');
+  }
+  return context;
+}