docs(security): Add Authentication & Authorization documentation

**Documentation Hub (1):**
- AUTHENT-AUTHORIT_README.md: Central hub for all security documentation
  - Quick navigation to authentication, authorization, and security guides
  - Overview of security features
  - Links to CQRS implementation details

**Security Implementation Guides (4):**
- API-SECURITY-IMPLEMENTATION-GUIDE.md: Complete security architecture
  - JWT Bearer authentication configuration
  - Token blacklisting with dual-cache strategy
  - Custom middleware (JwtBlacklistValidationMiddleware)
  - Rate limiting setup (60/min, 1000/hr)
  - CORS configuration
  - Security headers (XSS, Clickjacking, MIME-sniffing)
  - Polly resilience policies (Retry + Circuit Breaker)
  - External API security (ApiKeyHandler)
  - Production deployment checklist

- JWT_AUTHENTICATION_CQRS_ARCHITECTURE.md: CQRS authentication architecture
  - Command pattern (LoginUserCommand, BlacklistTokenCommand)
  - Query pattern (IsTokenBlacklistedQuery, GetTokenBlacklistStatsQuery)
  - MediatR integration and pipeline behaviors
  - Automatic caching with CachingBehavior
  - Handler implementations
  - Request flow diagrams
  - Best practices and patterns

- CQRS_LOGIN_IMPLEMENTATION_SUMMARY.md: Login implementation details
  - LoginUserCommand and handler breakdown
  - JWT token generation process
  - Validation and error handling
  - Response structure and metadata

- CQRS_LOGOUT_IMPLEMENTATION_SUMMARY.md: Logout implementation details
  - BlacklistTokenCommand and handler breakdown
  - Dual-cache token blacklisting strategy
  - Token invalidation process
  - Cache expiration and cleanup

**Key Topics Covered:**
- JWT Bearer authentication and authorization
- Token-based authentication (stateless)
- Role-based access control (RBAC)
- Token blacklisting and revocation
- CQRS pattern for authentication
- MediatR integration
- Dual-cache strategy (Memory + Distributed)
- Custom middleware for token validation
- Rate limiting and throttling
- CORS policies
- Security headers configuration
- API key management
- Polly resilience patterns
- External API security
- Production security checklist

This provides complete security documentation with CQRS implementation examples.

Author: dariemcarlosdev