feat(workflow-bar): processing-only elapsed timer + optimistic phase paint on resume

Timer now accumulates only while the harness works, pausing while a gate awaits
the reviewer and freezing when finalized (keyed per session, in-memory). Resume
now colours the re-entry phase immediately from the manifest's phase (1..8),
mirroring the F1 paint for new questions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/shell/AppShell.session-mgmt.test.tsx

@@ -82,6 +82,20 @@ test("Resume from the panel activates the session and closes the panel", async (
   await waitFor(() => expect(screen.queryByText("Domanda originale")).not.toBeInTheDocument()); // panel closed
 });
 
+test("Resume paints the re-entry phase from the manifest (optimistic, before the first gate)", async () => {
+  useSessionStore.getState().resetSession();
+  server.use(
+    http.post("http://localhost:8787/sessions/:id/resume", () => new HttpResponse(null, { status: 204 })),
+    http.get("http://localhost:8787/sessions/:id", () =>
+      HttpResponse.json({ id: "s1", status: "open", phase: 4 })),
+  );
+  wrap();
+  await userEvent.click(await screen.findByText("Attiva uno"));
+  await screen.findByText("Domanda originale"); // panel open
+  await userEvent.click(screen.getByRole("button", { name: /resume/i }));
+  await waitFor(() => expect(useSessionStore.getState().currentPhase).toBe("F4"));
+});
+
 test("a failed resume keeps the panel open and does not activate the session", async () => {
   server.use(http.post("http://localhost:8787/sessions/:id/resume", () => new HttpResponse(null, { status: 409 })));
   wrap();