feat: AI Code Governance CLI v1.0.0

- Config-driven gates via .codegov.yml/.codegov.json
- disclosure gate: requires AI-GENERATED/AI-ASSISTED markers on changed files
- rfc gate: requires issue/RFC reference in commit message or PR description
- checklist gate: requires all items checked in REQUIREMENTS.md
- quality gate: runs configurable lint/test/typecheck commands
- CLI with readable reports and non-zero exit on violations
- 41 tests covering all gates, config loading, and integration
- Zero skeletons, no fake features, deferred items honestly documented