fix(ui): title the workspace tab "Workspace", not the raw i18n key

DocumentTitle mapped /workspace to nav:run, a key that does not exist, so
i18next rendered the key itself and the browser tab read "run". Point it at
nav:workspace, which both locales already ship, and add a test asserting each
top-level route resolves to a translated label.

client/src/components/DocumentTitle.tsx

@@ -27,7 +27,7 @@ export function DocumentTitle() {
   } else if (path.startsWith("/workflows")) {
     title = t("workflows");
   } else if (path.startsWith("/workspace")) {
-    title = t("run");
+    title = t("workspace");
   } else if (path.startsWith("/settings")) {
     title = t("settings");
   } else if (path !== "/") {

client/src/components/__tests__/DocumentTitle.test.tsx

@@ -0,0 +1,39 @@
+/**
+ * @file DocumentTitle.test.tsx
+ * @description Guards the route→browser-tab-title map against missing i18n keys:
+ * a key that does not exist renders as the raw key (the "run" bug), so each route
+ * is asserted against its translated label.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { describe, it, expect, beforeAll } from "vitest";
+import { render } from "@testing-library/react";
+import { MemoryRouter } from "react-router-dom";
+import i18n from "i18next";
+import { DocumentTitle } from "../DocumentTitle";
+
+const titleFor = (path: string) => {
+  render(
+    <MemoryRouter initialEntries={[path]}>
+      <DocumentTitle />
+    </MemoryRouter>
+  );
+  return document.title;
+};
+
+describe("DocumentTitle", () => {
+  beforeAll(async () => {
+    await i18n.changeLanguage("en");
+  });
+
+  it("titles the workspace route with its nav label, not the raw key", () => {
+    expect(titleFor("/workspace")).toMatch(/^Workspace · /);
+  });
+
+  it("titles the other top-level routes", () => {
+    expect(titleFor("/")).toMatch(/^Dashboard · /);
+    expect(titleFor("/sessions")).toMatch(/^Sessions · /);
+    expect(titleFor("/workflows")).toMatch(/^Workflows · /);
+    expect(titleFor("/settings")).toMatch(/^Settings · /);
+  });
+});