Add development guide (dev.md)

Comprehensive development documentation including:
- Quick start guide (5 minutes setup)
- Complete setup instructions for all services
- MongoDB, Anvil, Backend, and Frontend setup
- Service overview and status checks
- Common development tasks
- Environment variable configuration
- Testing guidelines
- Debugging tips
- Dependency management
- Troubleshooting guide
- Development checklist

This file helps new developers get started quickly with the project.

Author: Stalin