Names, from the same graph as the network

Step 5 of the connectivity order. Every node's internal name resolves to its
overlay address, on every node, computed centrally because it needs every node
at once.

Under `.internal`, which IANA reserved for exactly this in 2024 -- a name there
can never collide with a public one, so an internal name that leaks into a
public resolver fails rather than reaching a stranger's machine. The suffix is
settable for a mesh that wants its own.

Delivered in the same declaration as the peer list rather than a second one. A
node holding the peers and not the names, or the reverse, is half on the
network for as long as that lasts.

This is not the /etc/hosts floor the design removes. That floor existed because
a node had to reach the mesh's database before its own DNS worked -- a fallback
for a circularity that is now gone. This is the mechanism: the complete set of
names, generated whole and owned by the mesh, rather than a patch written
underneath something else. A resolver daemon becomes necessary when names are
wanted that are not one-per-node, and that is not yet true.

A node resolves its own name to its overlay address rather than a loopback,
because a service binding to the name it was given would otherwise listen
somewhere nothing else can reach -- and the failure would appear on every other
machine rather than that one.

A node with no address gets no name. A name resolving to nothing is worse than
no name: connecting to an address that does not answer hangs, where a name that
does not resolve fails at once and says which name it was.

Found while writing it: a test asserting every file in the declaration is mode
0600 would have forced /etc/hosts to 0600 and broken every lookup on the
machine, to protect a file that is not secret.

Verified in the lab: three machines, nine name lookups, each resolving to the
right overlay address and reaching it.

cmd/mesh-control/main.go

@@ -620,7 +620,7 @@ func overlayPush(ctx context.Context, inv *inventory.Inventory) error {
 			fmt.Printf("%s is not on the overlay yet — skipped\n", n.Name)
 			continue
 		}
-		declaration, err := overlay.Declaration(n, peers, "")
+		declaration, err := overlay.Declaration(n, peers, nodes, "")
 		if err != nil {
 			return err
 		}