feat: Add Docker support for local development

[Ashvin-KS]

Problem

New contributors need to install Node.js, npm, and other dependencies manually.

Proposed Solution

Add Docker support:

• Dockerfile for development
• docker-compose.yml for easy setup
• README instructions for Docker

Benefits

• Consistent development environment
• Easier onboarding for new contributors
• No dependency conflicts

Implementation Notes

• Use Node.js 20 Alpine image
• Mount source code as volume
• Expose port 3000