feat(admin): 仪表盘次级概览卡接真数据(A5) — 8卡聚合,存储卡诚实占位

- Dashboard.tsx 去掉占位块 → OverviewSection; 新增 admin/modules/dashboard/(MiniMetric/useDashboardExtras/overviewMetrics/OverviewSection)
- 8卡用现有 lib/api 导出: LLM组/RAG文档/自动化/已装插件(含toolCount)/用户/网关请求/LLM调用+子代理/存储(缺只读端点→诚实占位)
- 端点报错→值'—'+徽标'端点报错'+hint后端原文(不崩不伪造)
- 仅碰 Dashboard.tsx+dashboard/*, 未动 api.ts/types.ts(避免并发冲突)
- 前端 npm run build 绿(156 modules)

frontend/web/src/admin/modules/dashboard/OverviewSection.tsx

@@ -0,0 +1,29 @@
+import type { ReactNode } from "react";
+import { Surface } from "../../../components/primitives";
+import { MiniMetric } from "./MiniMetric";
+import { buildOverviewMetrics } from "./overviewMetrics";
+import { useDashboardExtras } from "./useDashboardExtras";
+
+/** The secondary dashboard block: 资源 / LLM / 业务 aggregates pulled from the
+ *  real admin endpoints (design/10 §3 #1, §4). Each card drills down; the most
+ *  detailed view always lives on its own module page. */
+export function OverviewSection(): ReactNode {
+  const extras = useDashboardExtras();
+  const metrics = buildOverviewMetrics(extras);
+  return (
+    <Surface className="space-y-3">
+      <div className="flex flex-wrap items-center gap-2">
+        <h3 className="text-sm font-semibold">资源 / LLM / 业务概览</h3>
+        <span className="text-xs text-[var(--mu-text-lo)]">真实聚合 · 每卡可下钻</span>
+      </div>
+      <div className="grid grid-cols-1 gap-3 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4">
+        {metrics.map((m) => (
+          <MiniMetric key={m.label} {...m} />
+        ))}
+      </div>
+      <div className="pt-1 text-xs text-[var(--mu-text-lo)]">
+        卡片即入口，点击下钻到对应模块；缺端点的卡片只标注缺口，不伪造数值。
+      </div>
+    </Surface>
+  );
+}