default issue-implement to no-audit; make audit opt-in (#474) (#475)
Invert the audit default in issue-implement: no-audit is now the default path, and the local dual-agent audit handshake is engaged only when the human passes the word 'audit' as a skill argument. No CLI behavior changes; the skill simply drives vrg-pr-workflow with --no-audit by default. Frame the local audit mechanism as experimental in both issue-implement and issue-audit. The PR-phase audit after vrg-submit-pr is unaffected.