Introduces `--only-from-report` and `--only-keys` arguments to the `references` validation command.
These allow re-validating only specific citation keys, either from a previous validation report or a custom list.
This significantly improves the workflow for correcting references by enabling focused re-runs and reducing validation time.
Removes the standalone `README_REFERENCE_CHECK.md` documentation, as its content is now implicitly handled by the integrated CLI help and broader documentation.
