feat(workflow-bar): total elapsed timer after the phase circles

frontend/src/shell/ElapsedTimer.test.tsx

@@ -0,0 +1,17 @@
+import { render, screen } from "@testing-library/react";
+import { ElapsedTimer } from "./ElapsedTimer";
+
+test("renders nothing without a start time", () => {
+  const { container } = render(<ElapsedTimer startedAt={null} />);
+  expect(container).toBeEmptyDOMElement();
+});
+
+test("frozen elapsed when stoppedAt is set (2m 5s)", () => {
+  render(
+    <ElapsedTimer
+      startedAt="2026-07-03T10:00:00.000Z"
+      stoppedAt="2026-07-03T10:02:05.000Z"
+    />,
+  );
+  expect(screen.getByText("2m 5s")).toBeInTheDocument();
+});