feat: add integration and setup tests and complete code review fixes

design.md

@@ -285,9 +285,11 @@ local globalKey = KEYS[3]  -- global:stats
 
 ### Input Validation
 
-- **Event ID Validation**: Numeric constraints
-- **Request Rate Limiting**: DDoS protection
+- **Event ID Validation**: Numeric constraints with range checking
+- **Purchase ID Validation**: UUID format validation
+- **Request Rate Limiting**: Multi-tier DDoS protection
 - **Parameter Sanitization**: Injection prevention
+- **Request Size Limits**: Prevents large payload attacks
 
 ### Container Security
 
@@ -301,6 +303,14 @@ local globalKey = KEYS[3]  -- global:stats
 - **Audit Logging**: Purchase tracking
 - **Secure Defaults**: Production-ready configuration
 
+### Security Headers & Middleware
+
+- **Helmet.js**: Comprehensive security headers
+- **Content Security Policy**: XSS prevention
+- **HSTS**: HTTPS enforcement
+- **Frame Guard**: Clickjacking protection
+- **Security Logging**: Suspicious request monitoring
+
 ## Deployment Strategy
 
 ### Development Environment