Fill a preference's ${setting:} from its manifest default (hq ADR 0262)

Without a default, a running module could never gain a setting: the file asking for it
failed to compose until set, and the key was refused as stray until a file asked for it.
Defaults sit under the mesh's and the node's settings, never merge into a JSON file, are
refused for the operator's own values, and settings shows each value's source.

internal/catalogue/verbs.go

@@ -249,7 +249,9 @@ var ControllerVerbs = []Verb{
 		}, nil, "adopted"),
 		Replaces: []string{"mesh-controller token issue", "wg set"}},
 	{Name: "settings", Description: "Read or set what an assignment is configured with: a module's settings for the whole " +
-		"mesh, or for one machine. Without values or clear, answers the layer as it stands — read it before setting it; " +
+		"mesh, or for one machine. Without values or clear, answers the layer as it stands — read it before setting it — " +
+		"then every value the module gives a default or a layer sets, with where it comes from: the module's default, " +
+		"the mesh, or the machine (novox/hq ADR 0262); " +
 		"with history, the layers it replaced. Setting replaces that layer whole and answers each key it adds (+), " +
 		"changes (~) and removes (-); a set that would remove a key is refused unless replace says it is meant " +
 		"(novox/hq ADR 0217). Takes effect at the next push. With clear, removes the layer and the module is back to " +