[Admin Console] Phase 7: Operator notification backend (dispatch, channels, events, delivery log)

[Ferryx349]

Parent: #637

Summary

Ship the full server-side notification pipeline so operators can alert Discord, Telegram, Slack, or a generic HTTP webhook when important relay events happen.

Scope

Settings & validation

• admin.notifications section in settings and settings-config.ts validation
• enabled, targets[] (http | discord | slack | telegram), per-event toggles, retry policy
• Safe defaults: disabled, no targets

Dispatch core

• NotificationService.dispatch(eventType, payload) — non-blocking, must not stall hot paths
• Configurable retry (max attempts, backoff)
• Postgres delivery log (target, event, status, attempts, error snippet, timestamps) + retention default

Channel adapters

• Generic HTTP webhook (JSON envelope: event, relay, timestamp, data)
• Discord incoming webhook
• Slack incoming webhook
• Telegram bot API (token and chat id; mask secrets in logs)

Event hooks (from #637)

Event	Trigger
admission.invoice.created	PaymentsService.createInvoice
admission.invoice.paid	PaymentsService.confirmInvoice / admit
admission.invoice.failed	expired / failed invoice paths (define explicitly)
settings.changed	successful admin settings patch (redact secrets)
relay.restarted	startup once per deploy (avoid worker spam — document choice)

Tests

• Unit tests: validation, retry, adapters (mock HTTP), hook wiring