✅ Fix sign-up test race (#2422)

## AI Disclaimer

Using Codex with gpt-5.6-sol. Reviewed manually.

Author: tiangolo

frontend/tests/sign-up.spec.ts

@@ -79,15 +79,16 @@ test("Sign up with existing email", async ({ page }) => {
 
   await fillForm(page, fullName, email, password, password)
   await page.getByRole("button", { name: "Sign Up" }).click()
+  await expect(page).toHaveURL(/\/login$/)
 
   await page.goto("/signup")
 
   await fillForm(page, fullName, email, password, password)
   await page.getByRole("button", { name: "Sign Up" }).click()
 
-  await page
-    .getByText("The user with this email already exists in the system")
-    .click()
+  await expect(
+    page.getByText("The user with this email already exists in the system"),
+  ).toBeVisible()
 })
 
 test("Sign up with weak password", async ({ page }) => {