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.

.gitignore

@@ -204,6 +204,7 @@ dev_config.yaml
 reports/
 output/
 findings/
+*.sarif
 *.sarif.json
 *.html.report
 security_report.*
@@ -291,4 +292,5 @@ test_projects/*/wallet.json
 test_projects/*/.npmrc
 test_projects/*/.git-credentials
 test_projects/*/credentials.*
-test_projects/*/api_keys.*
+test_projects/*/api_keys.*
+test_projects/*/ci-*.sh