refactor: derive D004, F001, G001 reports from A003 settings data

- Add D004_SETTINGS, F001_SETTINGS, G001_SETTINGS constants for filtering
- Add generate_d004_from_a003, generate_f001_from_a003, generate_g001_from_a003 methods
- Add filter_a003_settings and extract_postgres_version_from_a003 helpers
- Add report_to_markdown method with report-specific markdown generators
- Add --format option to CLI (json/markdown/both)
- Update generate_all_reports to use A003 data for derived reports
- Update tests to reflect new architecture

Author: claude