feat: migrate Telegram Login Widget to v23 with admin-configurable settings

- Upgrade telegram-widget.js from v22 to v23 (TelegramLoginButton + ConnectedAccounts)
- TelegramLoginButton fetches widget config from API instead of hardcoded values
- Add TelegramWidgetConfig type and API method with fallback to env defaults
- Remove botUsername prop — now sourced from backend API
- Add useEffect cleanup to prevent orphaned iframes on unmount
- Add TELEGRAM_WIDGET category to admin interface settings menu
- Add i18n translations for widget settings (ru, en, zh, fa)

src/pages/Login.tsx

@@ -485,10 +485,7 @@ export default function Login() {
                   </p>
                 </div>
               ) : (
-                <TelegramLoginButton
-                  botUsername={botUsername}
-                  referralCode={referralCode || undefined}
-                />
+                <TelegramLoginButton referralCode={referralCode || undefined} />
               )}
             </div>