billing resource for plan retrieval and billing lifecycle actions.
Direct actions (handled locally): all, get, create, update, delete, calls, phones
Stripe-delegated actions (proxied to stripe-handler): checkout, billing-portal, update-subscription, sync, check-status, purchase-calls, cancel-calls, add-phone-number, remove-phone-number
The previously documented
plan, usage, and invoices action names do not exist — use get and all to retrieve billing data.