Apply one Paid customer-owned hostname

Requires Paid access (a Stripe period or a grant) or, for a Free workspace, a project that currently shows the powered-by flag, and no expired credit-exhaustion grace. Returns paid_plan_required otherwise, or insufficient_organization_credits after seven days with no available credits, without provider mutation. Top-ups lift a credit-exhaustion block but never start or extend Paid access. Without an active Prod deployment, apply declares the hostname as awaiting_deployment, enabling Cloudflare consent without provider resources, DNS changes or domain charges. After a successful Prod deployment, replay the same hostname and idempotency key to activate it. A changed request under a used key returns idempotency_key_reused (409).