Core hooks for regional compliance integrations: invoice.* events, delivery-failure alerting, webhook docs

[telivity-otaip]

Summary

Supports #159 (Brazilian government guest registration + tax invoice integrations). The existing webhook subscription system already covers the event-driven side; this PR adds the three core pieces that make external regional integrations clean to build, without putting any regional tax logic in core.

Supersedes #161 (same changes + README test-count sync that CI rejected on the previous branch).

1. Fiscal document references + invoice.* events

Jurisdictions like Brazil require official tax documents (NFS-e tax notes) per folio. Core now stores a reference to such documents and emits lifecycle events, while issuance stays in an external integration:

• New fiscal_documents table (property-scoped, folio-linked, metadata jsonb for regional fields — series, verification codes, etc. Core never interprets them).
• New events: invoice.requested, invoice.issued, invoice.voided.
• New endpoints on folios:
  • POST /folios/:id/fiscal-documents — request a document → emits invoice.requested
  • POST /folios/:id/fiscal-documents/:documentId/issue — integration reports the issued document number → emits invoice.issued
  • POST /folios/:id/fiscal-documents/:documentId/void — void/cancel → emits invoice.voided
  • GET /folios/:id/fiscal-documents — list
• All queries scoped by propertyId per the multi-tenancy rules; migration added to both push-schema.ts and src/migrations/0007_fiscal_documents.sql.

2. Staff alerting on permanent webhook delivery failure

A delivery that exhausted all 5 retries (~7h) previously went silent — unacceptable when the subscriber is a mandatory government-reporting integration. WebhookDeliveryService now emits an in-process webhook.delivery_failed event on permanent failure, and StaffNotificationListener creates a critical staff notification. The internal event is deliberately not fanned out to external subscribers (their endpoint is the thing failing), and failures of staff.notification_created deliveries are skipped to prevent an alert-on-alert loop.

3. Webhook integration guide (docs/webhooks.md)

Documents subscribing via the Connect API, HMAC signature verification (with code sample), the lean-payload / fetch-by-entityId convention (keeps guest PII out of webhook bodies), retry + at-least-once semantics, the polling reconciliation fallback, the fiscal document flow, and a worked government guest-registration example. Linked from the README. README test counts synced to 1129 / 136.

Testing

• 18 new tests (fiscal document lifecycle + multi-tenancy scoping, delivery-failure event emission, listener behavior incl. loop guard).
• Full suite: 1129 tests across 136 files. Typecheck clean, lint 0 errors.

Notes for reviewers

• The fiscal document concept is not in the KB; it is deliberately modeled as pure integration plumbing (a reference + lifecycle + events), not hotel/tax domain logic. documentType and metadata are opaque to core.
• EventEmitter2 is injected @Optional() into WebhookDeliveryService so existing direct-construction tests remain valid.