New webhook event: invoice.undeliverable — know when a recipient can't be reached

Now that delivery is Peppol-only, a recipient that cannot be found on the network ends the send in the no_action status — "Not Deliverable" in the dashboard. Until today only the dashboard showed it: webhook integrations, SDK polling and CI pipelines had no signal at all.

What changed

• New webhook event invoice.undeliverable. Fired when our provider reports that no receiving capability exists for the recipient. The payload has the same shape as the other invoice.* events and carries status: "no_action". Wildcard (*) subscriptions receive it automatically — add it to explicit event filters if you subscribe per-event.
• SDK: waitFor() fails fast. no_action is now a terminal failure alongside failed and rejected: the promise rejects immediately instead of polling until the timeout. Waiting for no_action as an explicit target still resolves.
• CLI: getpeppr send --watch exits non-zero. A watch ending on no_action now exits 1, so scripts and CI pipelines catch undeliverable invoices instead of reporting success.

Anything breaking?

No runtime breaking change. The /v1 status vocabulary is untouched — no_action already existed as a document status. Endpoints subscribed to specific events keep receiving exactly what they subscribed to; only wildcard (*) subscribers start receiving the new event. One note for TypeScript users: the SDK's WebhookEventType union gains a member, so an exhaustive switch over it needs a new case "invoice.undeliverable" when you upgrade. To check a recipient before sending, use the directory search or the x-validate-recipient header.