XY-1152: Implement Source Library and Memory Authority lifecycle model

[yvette-carlisle]

Summary

• add Source Library lifecycle metadata on source capture and persisted tombstone metadata on delete
• add Memory Authority correction lifecycle metadata and freshness readback in history snapshots
• add authoritative stale-candidate revalidation coverage and align the registered repo gate to cargo make checks

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make checks
• independent fresh-context review checkpoint: clean

Notes

• Historical benchmark evidence rows preserve the legacy singular check command through a narrow docs-check exception rather than a command alias.