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.

backend/toolbox/workflows/trufflehog_detection/metadata.yaml

@@ -0,0 +1,34 @@
+name: trufflehog_detection
+version: "1.0.0"
+vertical: secrets
+description: "Detect secrets with verification using TruffleHog"
+author: "FuzzForge Team"
+tags:
+  - "secrets"
+  - "trufflehog"
+  - "verification"
+
+workspace_isolation: "shared"
+
+parameters:
+  type: object
+  properties:
+    verify:
+      type: boolean
+      default: true
+      description: "Verify discovered secrets"
+
+    max_depth:
+      type: integer
+      default: 10
+      description: "Maximum directory depth to scan"
+
+default_parameters:
+  verify: true
+  max_depth: 10
+
+required_modules:
+  - "trufflehog"
+
+supported_volume_modes:
+  - "ro"