feat(web): trade detail modal with prices, fees, timestamps

- Click any trade row in history table to open detail modal
- Modal shows 6 sections: 概览, 时间, 价差, 手续费, 多仓, 空仓
- Entries and exits displayed with 6 decimal precision
- Fee entry/exit and total fee displayed
- Open/close timestamps with full date-time format
- Duration, scale count, total amount, exit reason
- Orders sub-table if available
- Escape key and overlay click to close

web/static/index.html

@@ -116,6 +116,19 @@
       </div>
     </section>
   </div>
+
+  <!-- Trade Detail Modal -->
+  <div id="trade-modal" class="modal-overlay" style="display:none">
+    <div class="modal-content">
+      <div class="modal-header">
+        <h2>📋 交易详情</h2>
+        <button class="modal-close" onclick="closeTradeDetail()">✕</button>
+      </div>
+      <div id="trade-detail-body">
+        <div class="loading">加载中...</div>
+      </div>
+    </div>
+  </div>
 </div>
 
 <script src="/static/app.js"></script>