Sets up a standalone test app with an owner user (separate from NBLOCKS_DASHBOARD). This is designed for external projects (e.g., bridge-svelte) that need their own test app to run E2E tests against. Idempotent — if the app already exists (by domain), returns the existing one. The app is never deleted between test runs. POST /account/test/playwright/setup-test-app Headers: x-playwright-api-key: <your-api-key> Body: { domain: string, appName: string, ownerEmail: string, ownerPassword?: string } Returns: { appId, domain, tenantId, userId, email, message }