feat: Add secret detection workflows and comprehensive benchmarking (#15)

Add three production-ready secret detection workflows with full benchmarking infrastructure:

**New Workflows:**
- gitleaks_detection: Pattern-based secret scanning (13/32 benchmark secrets)
- trufflehog_detection: Entropy-based detection with verification (1/32 benchmark secrets)
- llm_secret_detection: AI-powered semantic analysis (32/32 benchmark secrets - 100% recall)

**Benchmarking Infrastructure:**
- Ground truth dataset with 32 documented secrets (12 Easy, 10 Medium, 10 Hard)
- Automated comparison tools for precision/recall testing
- SARIF output format for all workflows
- Performance metrics and tool comparison reports

**Fixes:**
- Set gitleaks default to no_git=True for uploaded directories
- Update documentation with correct secret counts and workflow names
- Temporarily deactivate AI agent command
- Clean up deprecated test files and GitGuardian workflow

**Testing:**
All workflows verified on secret_detection_benchmark and vulnerable_app test projects.
Workers healthy and system fully functional.

docker-compose.yml

@@ -324,6 +324,8 @@ services:
     volumes:
       # Mount workflow code (read-only) for dynamic discovery
       - ./backend/toolbox:/app/toolbox:ro
+      # Mount AI module for A2A wrapper access
+      - ./ai/src:/app/ai_src:ro
       # Worker cache for downloaded targets
       - worker_secrets_cache:/cache
     networks: