add `service move` to transfer services between projects

[yigitkonur]

problem

there's no way to move a service (with its config, variables, volumes) from one project to another. this comes up when reorganizing infrastructure, splitting monolithic projects, or consolidating test services into a shared project.

real-world scenario

started with all services in one project during prototyping. now need to split the proxy service into its own project for independent scaling and billing. only option today is to recreate everything from scratch in the new project, manually copying all variables.

proposed solution

railway service move <service-name> --to-project <project-id>
railway service move <service-name> --to-project <project-id> --include-volumes

should transfer: service config, environment variables, domains, and optionally volumes.

considerations

• cross-project networking changes (internal domains would change)
• volume data migration complexity
• could start with config+vars only, add volume migration later