docs: Update documentation for Phase 3 features

Comprehensive documentation updates for v0.4.0:

Documentation Updates:
- Updated README.md with Phase 3 capabilities and features
- Updated STATUS.md to reflect v0.4.0 completion
- Updated CHANGELOG.md with Phase 3 features
- Created v0.4.0 release notes
- Updated docs/README.md with Phase 3 guides

New Phase 3 Guides:
- Kubernetes Support Guide: K8s manifest parsing and analysis
- REST API Guide: Complete API documentation and usage
- Real-time Monitoring Guide: WebSocket events and watch mode
- Advanced Agents Guide: Security agent development
- Compliance Frameworks Guide: CIS, NIST, PCI-DSS, SOC 2, GDPR

Phase 3 Features Documented:
- Kubernetes manifest support
- Real-time monitoring and events
- REST API server with OpenAPI
- Advanced security agents (lateral movement, data exfiltration, compliance)
- Compliance frameworks (CIS AWS Foundations, NIST 800-53, PCI-DSS, SOC 2, GDPR)
- Multi-IaC support enhancements

Testing Results:
- All Phase 3 agents tested and working
- Web server and API endpoints functional
- OpenAPI specification accessible
- Agent registry updated with new agents
- Compliance scanner generates 25 findings
- Lateral movement agent generates 3 findings
- Data exfiltration agent working (0 findings for mini-cloud)

Status: ✅ Phase 3 documentation complete
Next: v0.4.0 release preparation