fix(webhooks): wallet/transaction event emission, HMAC signing, retry/backoff queue

[priscaenoch]

Summary

Closes #480, closes #481, closes #482, closes #483.

Most of the webhook infrastructure required by these issues already existed on staging (event emission, HMAC signing, retry/backoff), but several files had unresolved merge conflicts — duplicated imports, orphaned code fragments, and missing methods — that left the webhooks module (and its transitive dependencies) unable to compile or pass its own tests. This PR repairs that damage and wires up the remaining behavior:

• Emit wallet created webhook after orchestration #480 wallet.created — wallets.service.ts already called WebhookEventEmitterService.emitWalletCreated after orchestration, but the file had duplicate imports and a duplicated/detached updateWalletStatus status-transition guard, plus two missing helper methods (toPublicWallet, archiveWallet) referenced by findAll/findOne/archive. Fixed and restored.
• Emit transaction confirmed webhook on status change #481 transaction.confirmed — transactions.service.ts already called emitTransactionConfirmed on status change, but create() had a syntactically broken emit call, a missing emitDomainEvent helper, and non-optional collaborators (webhook emitter/cache/metrics) that didn't match how tests construct the service. Fixed.
• Sign outbound webhook payloads with HMAC #482 HMAC signing — already correctly implemented in webhook-signer.service.ts / webhook-dispatch.service.ts (HMAC-SHA256, timestamped, constant-time verification). No changes needed there.
• Process webhook delivery queue with backoff #483 retry/backoff queue — already correctly implemented in webhook-retry.service.ts / webhook-dispatcher.service.ts / webhook-delivery-queue.worker.ts (exponential backoff, dead-letter after max attempts, periodic worker), but webhook-dispatcher.service.ts was missing a log helper and a maxRetries accessor that caused runtime failures in the exact delivery/backoff path this issue covers. Fixed (now delegates to WebhookRetryService.getMaxRetries()).

Also touched (forced by the same merge damage / build graph)

• webhook.service.ts / webhook.controller.ts: reconciled two duplicated CRUD implementations into one, restoring endpoint caching and WebhookFilterDto-based pagination/filtering.
• balance-indexer.service.ts / stellar-horizon.service.ts: transactions.service.ts imports BalanceIndexerService, so its merge damage blocked compilation of my actual target file. Reconciled to the BalanceRepository-based design that the existing (also-broken) test suite expects.
• health.controller.ts / health.module.ts: a duplicated controller/module definition here broke the overall nest build, unrelated to webhooks but blocking CI regardless.

Testing / validation performed

• npx tsc --noEmit — clean for every file touched in this PR.
• npx jest src/webhooks — all 9 webhook spec files pass (signing, dispatch, retry, config, feature-flag, request-id propagation, CRUD service, dispatcher).
• npx jest src/wallets/wallets.service.spec.ts — passes except one pre-existing, unrelated failure (see Risks).
• npx jest src/transactions/transactions.service.spec.ts — passes except 7 pre-existing, unrelated failures (see Risks).
• npx jest src/balance-indexer/balance-indexer.service.spec.ts — passes (16/16).
• npx prettier --check — clean on all touched files.

Risks / follow-ups (pre-existing, out of scope for this PR)

staging currently has extensive pre-existing breakage unrelated to these 4 issues that I deliberately left untouched per scope:

• transactions.service.spec.ts has 7 failing tests for a findAll filtering feature (assetType/assetCode/amount range/date range) that was never implemented — looks like unmerged work from a different ticket (Transactions API: Add filtering query params #341/Transactions API: Emit domain events #342 per branch history).
• wallets.service.spec.ts has 1 failing test where findAll's default archived-wallet exclusion doesn't match its own test's expectation — looks like fallout from the separate wallet-archive feature (PR Graceful shutdown, log redaction, and wallet archiving #617).
• balance-indexer.controller.spec.ts / balance-indexer.integration.spec.ts, plus several other unrelated suites (wallet-creation-orchestrator.*, limits.service.spec.ts, auth/*), fail for reasons unconnected to webhooks (missing DI providers, jest/babel parse errors, other pre-existing bugs).
• A full tsc --noEmit across the whole repo still reports errors in ~40 files outside this PR's scope (auth, api-keys, supertest version mismatch, etc.) — staging does not currently build clean end-to-end.

None of the above are touched by this PR; they predate it and are unrelated to issues #480-#483. Recommend separate tickets for each.

Links:

• Emit wallet created webhook after orchestration #480
• Emit transaction confirmed webhook on status change #481
• Sign outbound webhook payloads with HMAC #482
• Process webhook delivery queue with backoff #483

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