[Idea] mcs export/import for machine portability

[bguidolim]

Idea

To replicate a full mcs setup on a new machine, users currently need to manually `mcs pack add` each URL, then `mcs configure` each project. A single export file describing the full desired state would complete the Terraform analogy.

# Export current machine setup
mcs export > mcs-setup.yaml

# On new machine
mcs import mcs-setup.yaml

The export file would contain:

• All registered pack URLs, versions, refs
• Global component selections
• Optionally: per-project configurations

Not planned for v2.1.0 — captured for future consideration.