Configurable Server Port Implementation

This PR adds flexible port configuration capability to the server through environment variables.

Key Changes:

Implemented PORT environment variable support with a default of 8080
Added port validation logic (valid range: 1024-65535)
Updated Dockerfile to include PORT configuration
Added comprehensive test coverage for port configuration
Updated documentation with port configuration instructions

Benefits:

Improved deployment flexibility
Better error handling for invalid port configurations
Enhanced developer experience with clear documentation
Maintains backward compatibility with default port

This change supports more flexible deployment scenarios while maintaining secure defaults and proper validation.