Derive data protection from a module's declared data (hq ADR 0233)

A module's data section says what it keeps and how precious it is; the backup holder's lines,
binding stickiness, retirement on unassign and D13's conditions follow from it, so issue 273's
empty replacement is said and an unassigned module's data is remembered, not forgotten.

cmd/mesh-controller/main.go

@@ -170,6 +170,9 @@ func run() error {
 		return retireCommand(ctx, args[1:])
 	case "cleanup":
 		return cleanupCommand(ctx, args[1:])
+	// The data every machine declares, as the self-check last found it (novox/hq ADR 0233).
+	case "data":
+		return dataCommand(ctx, args[1:])
 	case "version":
 		fmt.Println(version)
 		return nil