fix(workbench): suppress unconfigured demo alerts

The not_configured branch previously promoted mock task failures into critical alerts. Return an explicit empty alert source so the exception badge reflects only actionable backend state.

tests/browser/operational-task-approval.e2e.ts

@@ -264,6 +264,14 @@ test("审批动作展示中文参数和证据，viewer 不可审批，冲突后
   };
 
   await page.goto("/");
+  const alertTrigger = page.getByRole("button", {
+    name: "查看异常处置面板，当前 0 条待复核工况"
+  }).first();
+  await expect(alertTrigger).toBeVisible();
+  await alertTrigger.click();
+  await expect(page.getByText("当前无待复核工况", { exact: true }).first()).toBeVisible();
+  await expect(page.getByText("来源：未配置告警源", { exact: true })).toBeVisible();
+  await page.keyboard.press("Escape");
   const reconnectNotice = page.locator("[data-sonner-toast]").filter({
     hasText: "业务同步正在重连"
   });