diff_results.py --audit rejects a folder name without saying what the audit is called #1150

Where: scripts/diff_results.py main() (--audit).

Current gap: Audits are named by the manifest (german_credit_lending) but people type the folder name. The error lists nothing to choose from, unlike load_audit(), which suggests close matches.

Repro:

$ python3 scripts/diff_results.py --audit "German Credit Lending"
error: unknown audit(s): German Credit Lending

Suggested approach: Print the known audit names and a difflib.get_close_matches suggestion, normalizing case, spaces and underscores.

Done when: the error names the audits that exist and suggests the right one, with a test.