fix(ui): 兑换页面 '人民币' → 'RMB/CNY'

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/trading/presentation/pages/trading_page.dart

@@ -411,7 +411,7 @@ class _TradingPageState extends ConsumerState<TradingPage> {
                 // const SizedBox(width: 8),
                 // _buildCurrencyChip(SettlementCurrency.og, 'OG'),
                 // const SizedBox(width: 8),
-                _buildCurrencyChip(SettlementCurrency.usdt, '人民币'),
+                _buildCurrencyChip(SettlementCurrency.usdt, 'RMB/CNY'),
                 // const SizedBox(width: 8),
                 // _buildCurrencyChip(SettlementCurrency.dst, 'DST'),
               ],