System seats are mesh-* (one, mesh-wide) or node-* (one per node). Renamed:
the-build-machine -> mesh-build-machine (+scope mesh), the-catalogue ->
mesh-catalog, the-dns-port -> node-dns-resolver, the-intrusion-prevention ->
node-intrusion-prevention, the-packet-filter -> node-packet-filter,
the-resolver-configuration -> node-resolver-config, the-uplink -> node-uplink.
Removed the-showcase from the set — it becomes the first module-defined seat.
A manifest may declare its own seats (DefinesSeats); a claim is a system seat,
a reserved mesh-*/node-* name the mesh does not define (refused), or a
module-defined seat valid only when the manifest declares it.
Deferred: the delivering registry seats (git, npm-package-registry,
the-artifact-store) and the-private-network (a scope + server/client model
change), per ADR 0121.