feat(frontend): 用量页面 UI 优化 - 合并格式/类型列、分析面板可折叠

- UsageRecordsTable: 合并 API 格式与类型为单列，缩减列宽使表格更紧凑
- MainLayout: 添加 header 级 Teleport 插入点供子页面注入操作按钮
- Usage: 用量分析面板改为可折叠，折叠状态持久化到 localStorage

frontend/src/layouts/MainLayout.vue

@@ -266,6 +266,8 @@
                 {{ crumb.label }}
               </span>
             </template>
+            <!-- 页面级操作插入点 -->
+            <div id="breadcrumb-actions" />
           </div>
         </div>
 
@@ -279,6 +281,8 @@
         </div>
 
         <div class="flex items-center gap-2">
+          <!-- Page-level header actions (right side) -->
+          <div id="header-actions-right" class="flex items-center" />
           <!-- Theme Toggle -->
           <button
             class="flex h-9 w-9 items-center justify-center rounded-lg text-muted-foreground hover:text-foreground hover:bg-muted/50 transition"