Add Docker support with multi-stage builds for frontend and agent

[lllahaye]

This PR adds Docker configuration to run both the Next.js frontend and Python langgraph agent in containers. Key additions include:

• Multi-stage Dockerfile for efficient builds
• Docker Compose configuration for easy orchestration
• Volume support for agent data persistence
• Comprehensive Docker documentation

These changes simplify environment setup and deployment while ensuring consistent behavior across development environments.

[vercel]

@lllahaye is attempting to deploy a commit to the CopilotKit Team on Vercel.

A member of the Team first needs to authorize it.