From the beginning, prep.sh scripts have started by creating the VM.

This may be a too restrictive approach. Consider a use case that involves both Rust (targeting WebAssembly) and npm. Currently, both of these are separate folders.

Instead:

• instruct the user to create the plain VM
• provide its name to the scripts via MP_NAME (as now); but take away the defaults (i.e. a name must exist; this means we might want to have it as $1 instead of env.var.. prep.sh web
• check for minimal parameters (CPU, memory) in the script; give a warning if headroom considered too low
• test manually that a npm + Rust setup is doable
• revisit the rust+emb etc. folders, to apply with this approach:
  • they'll expect a Rust base image, and curry their stuff on top

This simplifies the scripts.