Added repository health files

Added repository health and project maintenance files to improve code quality, collaboration, and deployment readiness. Included .gitignore, .editorconfig, CHANGELOG.md, SECURITY.md, CODE_OF_CONDUCT.md, .env.example, Dockerfile, and .dockerignore. These files help standardize development practices, document project policies, manage environment configurations, support containerized deployment, and ensure a cleaner, more maintainable repository structure without affecting existing application functionality.