feat(hub): background board poll every 5s with SSE snapshot updates

Co-authored-by: Cursor <cursoragent@cursor.com>

manual_trading_hub/static/index.html

@@ -48,7 +48,7 @@
       <div class="toolbar">
         <button type="button" id="btn-monitor-refresh" class="primary">立即刷新</button>
         <label class="chk-label">
-          <input type="checkbox" id="auto-monitor" checked /> 每 5 秒自动刷新
+          <input type="checkbox" id="auto-monitor" checked /> 后台每 5 秒聚合 · SSE 自动更新
         </label>
         <button type="button" id="btn-close-all" class="danger">全局紧急全平</button>
         <span class="toolbar-spacer"></span>
@@ -245,6 +245,6 @@
   <div id="toast"></div>
   <script src="https://unpkg.com/lightweight-charts@4.2.0/dist/lightweight-charts.standalone.production.js"></script>
   <script src="/assets/chart.js?v=20260528-hub-no-30m"></script>
-  <script src="/assets/app.js?v=20260603-hub-board-poll-fix"></script>
+  <script src="/assets/app.js?v=20260603-hub-board-sse"></script>
 </body>
 </html>