feat: Implement Data Exfiltration Detection Agent

Implements comprehensive data exfiltration detection agent for Phase 3:

Data Exfiltration Agent Features:
- Detects unencrypted storage across AWS, GCP, Azure, Kubernetes
- Identifies public storage buckets and containers
- Finds missing access logging and monitoring
- Analyzes overly permissive egress rules
- Detects unencrypted backup storage
- Evaluates data retention policies
- Supports multiple vantage points (internal, external, IAM)

Core Components:
- agent.py: Main agent with vantage-aware analysis
- storage_analyzer.py: Storage security analysis engine
- network_analyzer.py: Network egress analysis engine
- test_agent.py: Comprehensive test suite (17 tests)
- requirements.txt: Dependencies (cloudsafeguard-sdk)
- README.md: Complete documentation and usage guide

Storage Analysis Capabilities:
- Multi-cloud support (AWS, GCP, Azure, Kubernetes)
- Encryption detection (at rest, in transit, key management)
- Public access analysis (ACLs, policies, endpoints)
- Access logging verification (CloudTrail, VPC Flow Logs)
- Backup security analysis (encryption, key management)
- Data retention policy evaluation (lifecycle, versioning)

Network Analysis Capabilities:
- Egress rule analysis (security groups, firewall rules)
- Destination analysis (CIDR blocks, IP ranges)
- Port analysis (port ranges, wildcard ports)
- Internet access detection (public IPs, gateways)
- Traffic monitoring verification (flow logs, watchers)

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

Testing Results:
- All 17 unit tests passing
- Successfully executed against mini-cloud example
- Proper error handling and vantage point filtering
- Fixed cidr_blocks vs destination_cidr_blocks compatibility

Files Created:
- agents/python/examples/data_exfiltration/agent.py
- agents/python/examples/data_exfiltration/storage_analyzer.py
- agents/python/examples/data_exfiltration/network_analyzer.py
- agents/python/examples/data_exfiltration/test_agent.py
- agents/python/examples/data_exfiltration/requirements.txt
- agents/python/examples/data_exfiltration/README.md

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

Status: ✅ Complete and tested
Next: Compliance Scanner Agent implementation