docs: add comprehensive codebase audit and redact remaining secrets

Audit Report:
- Complete codebase analysis (129 files, 40K LOC)
- Identified critical refactoring priorities
- Documented architectural strengths and weaknesses
- Created production readiness checklist
- Estimated 16-25 hours for core improvements

Key Findings:
- Type definition chaos (multiple Organization types)
- Massive service files (1,162 lines largest)
- Documentation sprawl (9 root markdown files)
- Configuration complexity (12+ config files)
- Zero colocated tests in src/

Security:
- Redacted full API keys from SECURITY_INCIDENT.md
- Only showing prefixes for reference
- All actual keys removed from repository

Next Steps:
- See CODEBASE_AUDIT_REPORT.md for detailed recommendations
- Priority: Fix Organization type conflicts
- Priority: Split large service files
- Priority: Rotate exposed API keys

Author: claude