Feat/add outbox event relay and handler registry

[Ezeh20]

Closes #153

Summary

The outbox from #122 had a complete producer side but only one consumer, bound directly to wallet provisioning. This adds a registry and a relay that leases any pending event and dispatches it by eventType, so domains subscribe to events instead of shipping a worker each.

• Handler interface keyed by eventType + eventVersion
• Registry rejects duplicate handler names, handlers for unknown event types, and emitted event types with no handler. All at startup
• Relay materialises one JobAttempt per (event, handler), leases via job-lease.service.ts, and dispatches
• An event is PUBLISHED only once every handler for its type succeeds; one failing handler doesn't block other types
• Exhausted events dead-letter; pnpm outbox:replay list|replay <id> is the operator path
• Wallet provisioning is now event-driven and src/workers/wallet-provisioning.worker.ts is deleted
• Subscribe-to-events flow documented in docs/domains/REQUEST_AND_EVENT_FLOWS.md

Evidence

pnpm relay:verify

A. Dispatch by event type
[relay] dispatched UserCreated v1 -> wallet.reserve-on-user-created
[relay] dispatched WalletProvisioningRequested v1 -> wallet.provision
  UserCreated                  PUBLISHED    wallet.reserve-on-user-created=COMPLETED
  WalletProvisioningRequested  PUBLISHED    wallet.provision=COMPLETED

B. Event type with no registered handler
[relay] no handler registered for ModuleCompleted v1; dead-lettering event ...
  relay summary: {"materialized":0,"dispatched":0,"failed":0,"unhandled":1}
  ModuleCompleted -> DEAD_LETTER (dead-lettered, not left PENDING)

C. Failing handler dead-letters, then replays cleanly
[relay] handler wallet.reserve-on-user-created failed ... attempt 5: CUSTODIAL_CONSENT_REQUIRED
  event -> DEAD_LETTER
  Operator grants the missing consent, then replays:
  event -> PUBLISHED

D. Re-delivering an already-published event is idempotent
  wallets for user: 1 before re-delivery, 1 after; provisioning jobs: 1