Judge tests that read another repository against what the check clones, never the desktop's checkout (issue 432)

Tests that read ../../../mesh-catalog or ../../../mesh-host gave a verdict
that depended on what sat beside the checkout: a stale or dirty sibling
failed them on a desktop, and a missing one skipped them unseen. They now
read the clone the build seat puts in MESH_CHECK_BESIDE, failing when it is
absent there, and elsewhere a copy captured at a named commit.

The skip had hidden that the builder test read a module retired by ADR 0190.
The systemd reading test no longer counts the machine's own environment.d.

cmd/mesh-controller/check_test.go

@@ -6,8 +6,10 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/novox/mesh-controller/internal/catalogue"
 	"testing"
+
+	"github.com/novox/mesh-controller/internal/beside"
+	"github.com/novox/mesh-controller/internal/catalogue"
 )
 
 // The check anybody can run is the check registration runs (novox/hq issue 148, ADR 0037): a manifest
@@ -56,10 +58,7 @@ func TestModuleCheckJudgesBetweenTheManifestsGiven(t *testing.T) {
 
 // The real catalogue passes the command, the way it passes the test that used to be the only check.
 func TestModuleCheckPassesTheCatalogue(t *testing.T) {
-	root := filepath.Join("..", "..", "..", "mesh-catalog", "modules")
-	if _, err := os.Stat(root); err != nil {
-		t.Skipf("catalogue sibling not present: %v", err)
-	}
+	root := beside.Catalogue(t)
 	paths, err := manifestsUnder(root)
 	if err != nil || len(paths) == 0 {
 		t.Fatalf("no manifests under %s: %v", root, err)