Rename the mesh's seats to mesh-*, keeping their interfaces

novox/hq ADR 0118: the prefix is the reservation rule, so a module
declaring any mesh-* name is refused and there is no reserved-names list to
drift. Ten seats renamed in the table, the manifests that claim them, the
controller's own shipped manifests, and the tests.

Not the migration 0118 expected: a holding is derived at resolution from
manifests and never stored, so nothing recorded points at an old name. A
kept rename table tells a manifest written against one what it became —
kept rather than retired, because a module lives in its own repository and
may be registered long after the catalogue stopped using it.

**A seat is not the interface it delivers.** The git seat became mesh-git
and the git provision did not; likewise the package registry. A blanket
replace renamed both, and the failure read "the package registry is served
on <nil>", which does not say "you renamed an interface". A test now pins
every seat against what it delivers, and that neither name is also the
other.

internal/overlay/generator.go

@@ -52,7 +52,7 @@ const Addressing = "mesh-addressing"
 // for two different purposes. Being **the** one the mesh runs over is singular, and without
 // saying so a person who chose a different VPN can still end up with this one dragged back in by
 // something that needed the mesh's own addresses. Which is exactly what happened, once.
-const TheNetwork = "the-private-network"
+const TheNetwork = "mesh-private-network"
 
 // **A resolver's data went the same way as the names.** Two constants used to sit here — a
 // `mesh-resolver` module that would write the machines as wildcards, and a `resolver-data`