feat(i18n): add Indonesian (Bahasa Indonesia) language support (#1399)

- Add 'id' to Language type in translations.ts
- Add ~1000 Indonesian translation keys covering all UI sections
- Update LanguageContext to persist 'id' in localStorage
- Add ID button to Header.tsx language toggle
- Add �� option to HeaderBar.tsx desktop dropdown and mobile toggle
- Add Indonesian translations to inline text objects in
  LoginRequiredOverlay, StrategyMarketPage, PositionHistory

Closes #XX

web/src/contexts/LanguageContext.tsx

@@ -14,7 +14,7 @@ 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'
+    return saved === 'en' || saved === 'zh' || saved === 'id' ? saved : 'en'
   })
 
   // Save language to localStorage whenever it changes