test: Add secret detection benchmark dataset and ground truth

Add comprehensive benchmark dataset with 32 documented secrets for testing
secret detection workflows (gitleaks, trufflehog, llm_secret_detection).

- Add test_projects/secret_detection_benchmark/ with 19 test files
- Add ground truth JSON with precise line-by-line secret mappings
- Update .gitignore with exceptions for benchmark files (not real secrets)

Dataset breakdown:
- 12 Easy secrets (standard patterns)
- 10 Medium secrets (obfuscated)
- 10 Hard secrets (well hidden)

test_projects/secret_detection_benchmark/config/settings.py

@@ -0,0 +1,21 @@
+"""
+Application settings and configuration
+"""
+
+# EASY SECRET #2: GitHub Personal Access Token
+GITHUB_TOKEN = "ghp_vR8jK2mN4pQ6tX9bC3wY7zA1eF5hI8kL"
+
+# EASY SECRET #3: Stripe API key
+STRIPE_SECRET_KEY = "sk_live_51MabcdefghijklmnopqrstuvwxyzABCDEF123456789"
+
+# Application settings
+DEBUG = False
+LOG_LEVEL = "INFO"
+
+# EASY SECRET #4: Database password
+DATABASE_CONFIG = {
+    "host": "prod-db.example.com",
+    "port": 5432,
+    "username": "admin",
+    "password": "ProdDB_P@ssw0rd_2024_Secure!"
+}