feat: add history report switcher dropdown in report detail view

webapp/static/index.html

@@ -103,6 +103,14 @@
 
       <!-- 报告详情视图 -->
       <section class="view" id="view-report" hidden>
+        <!-- 历史报告切换下拉（顶部，始终可见） -->
+        <div class="report-switcher no-print" id="report-switcher">
+          <label class="report-switcher-label">切换报告</label>
+          <select class="select report-switcher-select" id="report-switcher-select">
+            <option value="">— 加载中… —</option>
+          </select>
+        </div>
+
         <div class="empty" id="report-empty">
           <p>请先从「运行列表」选择一次运行。</p>
         </div>