补齐缓存写量与请求轮廓记账，便于核对提示缓存是否真的命中。

给用量行挂上轮次步骤和分段字数，统计页能看出缓存断在哪。

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

web/stats.html

@@ -117,12 +117,13 @@
             <thead>
               <tr>
                 <th scope="col">时间</th>
+                <th scope="col">步骤</th>
                 <th scope="col">caller</th>
                 <th scope="col">model</th>
                 <th scope="col" class="num">prompt</th>
-                <th scope="col" class="num">completion</th>
-                <th scope="col" class="num">total</th>
+                <th scope="col" class="num">未缓存</th>
                 <th scope="col" class="num">cached</th>
+                <th scope="col">断开</th>
                 <th scope="col" class="num">花销</th>
               </tr>
             </thead>