Idempotently ensures a plan exists (create-if-absent) for test scenarios. Unlike create-plan, when the plan already exists this returns it WITHOUT re-running the Stripe price sync/archive sweep. Used by specs that need a STABLE, reusable plan (e.g. welcome-paywall) whose Stripe price is synced once and reused — eliminating the create-then-checkout price-sync race. POST /account/test/playwright/ensure-plan Headers: x-playwright-api-key: <your-api-key> Body: { appDomain: string, key: string, name?: string, trial?: boolean, trialDays?: number, prices?: Price[] } Returns: { planId, key, name, created }