Name the paths a seat's holder owns, and refuse a claim or a declaration without the seat (issue 412)

Which module owns /etc/hosts or /etc/resolv.conf on a machine was answered only by reading every
manifest, and a module not holding node-hostname could declare /etc/hosts where nobody held it.
hq ADR 0287 makes the paths part of the seat's definition: node-hostname names /etc/hosts and
/etc/hostname, node-uplink names /etc/resolv.conf stepping back for node-resolver, node-resolver
names /etc/resolv.conf.

CanHold refuses a holder that does not declare every path (registration and handover), registration
refuses a module declaring a seat's path while claiming none of the seats naming it, a module's own
seat names paths under the same rules (node only, literal, not named by another seat), composition
refuses a generated resource on a seat's path, the uplink's step-back is read from the seat instead
of a special case, and `seats` shows each seat's paths and who owns each on each machine.

cmd/mesh-controller/seats_test.go

@@ -74,3 +74,22 @@ func TestAKindedBenchIsNotHandedOver(t *testing.T) {
 		}
 	}
 }
+
+// The listing shows each seat's paths, and the seat a path steps back for (novox/hq ADR 0287).
+func TestTheSeatsListingShowsEachSeatsPaths(t *testing.T) {
+	rows, _ := seatsHeld(catalogue.Seats(), nil)
+	got := map[string]string{}
+	for _, r := range rows {
+		got[r.Seat] = seatPathsText(r.Paths)
+	}
+	for seat, want := range map[string]string{
+		"node-hostname":      "/etc/hosts, /etc/hostname",
+		"node-uplink":        "/etc/resolv.conf (steps back for node-resolver)",
+		"node-resolver":      "/etc/resolv.conf",
+		"node-packet-filter": "—",
+	} {
+		if got[seat] != want {
+			t.Errorf("%s lists its paths as %q, not %q", seat, got[seat], want)
+		}
+	}
+}