feat: Add gitignore for backend project

Added backend-focused .gitignore rules to exclude unnecessary, generated, and sensitive files from version control.

Changes Ignored Node.js dependencies (node_modules/) Ignored environment configuration files (.env) Ignored log files and runtime data Ignored code coverage and build output directories Ignored editor and IDE-specific files Ignored operating system-generated files Ignored local cache and temporary files Purpose

To maintain a clean repository, improve security by preventing accidental commits of sensitive data, and reduce unnecessary files in version control.

Impact No functional changes to the application No API or database modifications Development and deployment workflows remain unaffected