feat: Implement Compliance Scanner Agent

Implements comprehensive compliance scanner agent for Phase 3:

Compliance Scanner Agent Features:
- CIS AWS Foundations Benchmark compliance checking
- NIST 800-53 control gap analysis
- PCI-DSS requirement validation
- SOC 2 control assessment
- GDPR compliance verification
- Supports multiple vantage points (iam-restricted, internal, external)

Core Components:
- agent.py: Main agent with framework-aware analysis
- frameworks/cis_aws.py: CIS AWS Foundations Benchmark checker
- frameworks/nist_800_53.py: NIST 800-53 control checker
- frameworks/pci_dss.py: PCI-DSS requirement checker
- test_agent.py: Comprehensive test suite (18 tests)
- requirements.txt: Dependencies (cloudsafeguard-sdk)
- README.md: Complete documentation and usage guide

CIS AWS Foundations Benchmark:
- Identity and Access Management (1.1-1.11)
- Logging and Monitoring (2.1-2.4, 3.1-3.14)
- Network Security (4.1-4.4)
- Storage Security (5.1-5.4, 6.1-6.50)
- Root account usage, MFA enforcement, password policies
- CloudTrail configuration, CloudWatch alarms
- Security group rules, SSH/RDP restrictions
- EBS encryption, S3 public access controls

NIST 800-53 Controls:
- Access Control (AC) family: Account management, least privilege
- Audit and Accountability (AU) family: Audit events, log protection
- System and Communications Protection (SC) family: Boundary protection, encryption
- System and Information Integrity (SI) family: Malicious code protection, monitoring
- Control gap analysis with remediation guidance
- Compliance scoring and percentage calculation

PCI-DSS Requirements:
- Network Security (Req 1, 4): Firewall, encryption in transit
- System Security (Req 2, 5, 6): Default passwords, anti-virus, secure systems
- Data Protection (Req 3): Encryption at rest
- Access Control (Req 7, 8): Business need-to-know, unique IDs
- Monitoring (Req 10): Audit logging and access tracking
- Physical Security (Req 9): Physical access controls
- Security Testing (Req 11): Regular security testing
- Security Policy (Req 12): Information security policy

Agent Registry Integration:
- Registered in internal/orchestrator/agent_registry.go
- Supports iam-restricted, internal, and external vantage points
- Enabled by default for compliance analysis

Testing Results:
- All 18 unit tests passing
- Successfully executed against mini-cloud example
- Generated 25 compliance findings (violations and gaps)
- Proper error handling and vantage point filtering

Files Created:
- agents/python/examples/compliance_scanner/agent.py
- agents/python/examples/compliance_scanner/frameworks/cis_aws.py
- agents/python/examples/compliance_scanner/frameworks/nist_800_53.py
- agents/python/examples/compliance_scanner/frameworks/pci_dss.py
- agents/python/examples/compliance_scanner/test_agent.py
- agents/python/examples/compliance_scanner/requirements.txt
- agents/python/examples/compliance_scanner/README.md

Files Modified:
- internal/orchestrator/agent_registry.go (added compliance_scanner agent)

Status: ✅ Complete and tested
Next: Documentation updates and v0.4.0 release preparation