Creates a tenant/user in an existing app WITHOUT linking to a separate app. Use this to test "new user signup" flow before they create their first app. POST /account/test/playwright/create-tenant-user Headers: x-playwright-api-key: <your-api-key> Body: { appDomain: string, email: string, password?: string, tenantName?: string, firstName?: string, lastName?: string } Returns: { tenantId, userId, email, message }