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 !== "/") {