Scenarios: egress where images are needed, and images: cut to what is ours

Every scenario that places a container runtime gives each of its machines
`egress: true` — a node that runs modules pulls images from the internet, which is what
a node does. The underlay-only scenarios (bootstrap-single, behind-nat,
segmented-and-unforwardable, the-ordinary-shape, two-on-a-segment) stay sealed on
purpose: an extra NIC would change the very reachability they are asserting about.

`images:` keeps only the mesh's own — 55 third-party entries leave whole-mesh-full
alone, and the machine fetches them itself by the digest its module.json already pins.
The whole-mesh beds also say per machine which of ours they get: novox the substrate
control plane and its own fifteen runtimes, ace its twenty-four, the two workstations
one each. That is not a lab economy. An operator's workstation holds the images its own
modules need, and giving these two the union would put some thirty gigabytes onto a
thirty-gigabyte disk.

bootstrap-with-registry.yml is deleted. It existed only to demonstrate the lab's
registry, nothing referenced it, and there is nothing left for it to demonstrate.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

README.md

@@ -194,7 +194,7 @@ the machines instead:
 
 ```sh
 incus list -c ns
-incus exec <instance>-registry -- systemctl is-active docker
+incus exec <instance>-anchor -- systemctl is-active docker
 ```
 
 *"I cannot see progress" is not evidence of no progress.*