fix(email): prevent ambiguous delivery blind re-dispatch

[kjxcodez]

Problem

VALID_DELIVERY_TRANSITIONS in �pps/api/src/repositories/email-delivery/email-delivery.repository.ts allows transitions from AMBIGUOUS -> SENDING and FAILED -> SENDING. This permits
eserveDelivery() to reclaim an ambiguous delivery and re-dispatch an outbound message without verifying provider-side acceptance, violating the invariant: 'Never blindly resend when provider acceptance is uncertain.'

Solution

1. Remove unsafe direct AMBIGUOUS -> SENDING transition without reconciliation verification.
2. Require reconciliation confirmation before re-dispatching ambiguous deliveries.
3. Add focused tests proving blind re-dispatches are prevented.

Dependencies

Depends on #32.