[bercianor]

Summary

• Import historical Mongock audit entries through AuditHistoryAppender, preserving history independently of live audit and journal writes.
• Propagate append failures with the change ID, destination stage, target system, and original cause.
• Extend the MongoDB import audit snapshot assertions and remove the DynamoDB test tied to live journal publication during import.

Testing

• Added a unit test covering append failure diagnostics and preservation of the original cause.
• Extended MongoDB integration coverage with the expected persisted audit sequence.
• Tests were not rerun for this PR; automated validation remains pending CI.