refactor(ui): 兑换页面文案调整

- 标题"积分股交易"改为"积分股兑换"
- "当前积分股价格"改为"当前积分股价值"
- 移除价格前的¥符号

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

frontend/mining-app/lib/presentation/pages/trading/trading_page.dart

@@ -125,7 +125,7 @@ class _TradingPageState extends ConsumerState<TradingPage> {
       padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 12),
       child: Center(
         child: Text(
-          '积分股交易',
+          '积分股兑换',
           style: TextStyle(
             fontSize: 18,
             fontWeight: FontWeight.bold,
@@ -158,7 +158,7 @@ class _TradingPageState extends ConsumerState<TradingPage> {
         crossAxisAlignment: CrossAxisAlignment.start,
         children: [
           Text(
-            '当前积分股价格',
+            '当前积分股价值',
             style: TextStyle(
               fontSize: 12,
               fontWeight: FontWeight.w500,
@@ -172,7 +172,6 @@ class _TradingPageState extends ConsumerState<TradingPage> {
               AmountText(
                 amount: priceInfo != null ? formatPrice(price) : null,
                 isLoading: isLoading,
-                prefix: '\u00A5 ',
                 style: const TextStyle(
                   fontSize: 30,
                   fontWeight: FontWeight.bold,