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.

internal/catalogue/resolve.go

@@ -957,7 +957,9 @@ func checkResources(modules []Manifest) []string {
 	// Judged as the machine composes them: where the node-resolver holder writes the resolver file, the
 	// uplink holder's rendering of it is not composed, so it is not a second owner (novox/hq ADR 0247).
 	modules = steppedBack(modules)
-	var problems []string
+	// And only a claimant of a seat naming a path declares it — the controller's generated resources
+	// included, which are judged here at composition (novox/hq ADR 0287).
+	problems := seatPathsOnMachine(modules)
 	owner := map[string]string{}
 	ownedPath := map[string]string{} // path → owning module, for the access check below
 	packagePresent, packageAbsent := map[string][]string{}, map[string][]string{}