feat: add SQLite persistent storage for request logging

- Add SQLAlchemy-based database layer for persistent storage
  - Create models for access_logs, credential_attempts, attack_detections, ip_stats
  - Include fields for future GeoIP and reputation enrichment
  - Implement sanitization utilities to protect against malicious payloads
  - Fix XSS vulnerability in dashboard template (HTML escape all user data)
  - Add DATABASE_PATH and DATABASE_RETENTION_DAYS config options
  - Dual storage: in-memory for dashboard performance + SQLite for persistence

  New files:
  - src/models.py - SQLAlchemy ORM models
  - src/database.py - DatabaseManager singleton
  - src/sanitizer.py - Input sanitization and HTML escaping
  - requirements.txt - SQLAlchemy dependency

  Security protections:
  - Parameterized queries via SQLAlchemy ORM
  - Field length limits to prevent storage exhaustion
  - Null byte and control character stripping
  - HTML escaping on dashboard output

.gitignore

@@ -61,6 +61,10 @@ secrets/
 *.log
 logs/
 
+# Database
+data/
+*.db
+
 # Temporary files
 *.tmp
 *.temp