fix(email): preserve DSN failure classification during reconciliation

[kjxcodez]

Problem

In �pps/api/src/services/email/reconciliation.service.ts line 707, when an asynchronous DSN bounce notification arrives from mailer-daemon@googlemail.com, pollInbound() hardcodes ailureCategory: EmailFailureCategory.INVALID_RECIPIENT, completely discarding the canonical category parsed by parseDsnReport() (such as SPAM_REJECTION, POLICY_REJECTION, RATE_LIMIT, SOFT_BOUNCE).

Solution

1. Preserve dsnReport.classification.category when updating EmailDeliveryModel.
2. Map canonical BounceCategory to appropriate EmailFailureCategory.
3. Add focused regression tests.

Dependencies

Depends on #32 and #33.