fix(#163,#162): list_credits status filter defaults to Active + retire event ordering

[akindoyinabraham0-collab]

Closes #163
Closes #162

Summary

Two bugs fixed in a single branch.

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Fix #163 — list_credits defaults to Active-only

Root cause: listCredits in credits.service.ts built its candidate list from a hardcoded empty array, so every filter — including the status filter — was dead code. The endpoint always returned an empty result set.

Changes:

• credit.repository.ts — added findByStatus(status, page, limit) to ICreditRepository and InMemoryCreditRepository.
• credits.service.ts — listCredits now reads from creditRepo.findByStatus(), defaulting to CreditStatus.Active when no status query param is supplied. Secondary filters (methodology, geography, vintageYear, tonnes range) are applied in-memory on top.
• credit.repository.spec.ts — six new tests covering every CreditStatus value (Active, Retired, Flagged, Pending), the empty-result case, and pagination.

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Fix #162 — retire emits CreditRetired only after record is persisted

Root cause: No explicit application-level event emission existed, but the method needed a clear enforced ordering guarantee so any future listener could never observe a CreditRetired event without a corresponding record in storage.

Changes:

• retirement.service.ts — introduced IEventEmitter interface and EVENT_EMITTER injection token. retire() now explicitly emits CreditRetired after retirementRepo.save() resolves. If the save throws, the event is never emitted. Ordering guarantee documented in JSDoc.
• retirement.module.ts — provides a Node.js EventEmitter instance bound to EVENT_EMITTER (no new npm dependency).
• retirement.service.spec.ts — new test file with six tests: save-before-emit order, record exists at emit time, no event on write failure, exactly one event per call, correct payload, record retrievable after retire.

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