Make standalone Credential records the sole durable certificate-content
authority and replace embedded CaRecord credentials with stable
credential ID references.
Rework snapshot export and restore to stream certificate content,
mint target-store references, preserve dependency ordering, and reject
legacy embedded-credential and v2 persistence formats.
Validated:
- lib tests: 516/516
- FilesystemPkiStoreTest: 16/16
- PMD and JavaDoc pass
- app compilation passes
- only the 29 independently classified revocation fixture failures remain