fix(demo): wait for post-login redirect before navigating in e2e tests

Two demo-guide.spec.ts tests navigated straight to /scenarios right after
clicking a login button without waiting for the /dashboard redirect to
settle first. This raced harmlessly on localhost but flaked against the
higher-latency Unraid deployment, hitting RequireAuth before the session
was confirmed.

frontend/e2e/demo-guide.spec.ts

@@ -13,6 +13,7 @@ test("scenario overview lists all 5 scenarios, ready right after a reset", async
   await resetDemoData(request);
   await page.goto("/login");
   await page.getByRole("button", { name: "Verken als Operations Manager" }).click();
+  await expect(page).toHaveURL(/\/dashboard$/);
   await page.goto("/scenarios");
 
   await expect(page.getByRole("heading", { name: "Probeer een demonstratiescenario" })).toBeVisible();
@@ -27,6 +28,7 @@ test("scenario overview lists all 5 scenarios, ready right after a reset", async
 test("starting a scenario navigates to its fixed record", async ({ page }) => {
   await page.goto("/login");
   await page.getByRole("button", { name: "Verken als Operations Manager" }).click();
+  await expect(page).toHaveURL(/\/dashboard$/);
   await page.goto("/scenarios");
 
   const duplicateCard = page.locator(".scenario-card", { hasText: "dubbele klant" });