Populate the previously empty `virtual_machines` map in the production environment. This defines a new "monitoring" VM instance running Debian with 2 cores, 4GB RAM, and 30GB disk space, assigned to IP 192.168.1.161.
- Remove `*.tfvars` from .gitignore to allow tracking variable files.
- Enforce Terraform version to be greater than or equal to 1.5.0 in prod configuration.