Say a layer whole where the mesh reports it, and give tests their placement (issue 651)

The facts snapshot, the take preview and the settings history read a layer as it
was set; tests that place give the layer through LayerOf.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

cmd/mesh-controller/modules.go

@@ -537,6 +537,10 @@ func settingsCommand(ctx context.Context, args []string) error {
 				if p.SetBy != "" {
 					by = "; " + p.SetBy
 				}
+				if p.Why != "" {
+					// A layer whose placement moved out of it (migration 0097): still the layer, as it stands.
+					by += "; " + p.Why
+				}
 				fmt.Printf("%s on %s, until %s (%s%s):\n  %s\n", positionals[0], where,
 					p.ReplacedAt.Local().Format("2006-01-02 15:04:05"), p.ReplacedBy, by, shown)
 			}