Rename configuration selection to overlays

internal/core/config/load.go

@@ -10,7 +10,7 @@ import (
 // boundary. It is intentionally narrow: configuration discovery and CLI flag
 // parsing remain outside this package.
 type LoadOptions struct {
-	Profile             string
+	Overlay             string
 	Overrides           []configkit.Override
 	InvocationDirectory string
 }
@@ -30,7 +30,7 @@ func loadDocumentWithSource(source configkit.Source, options LoadOptions, import
 	return configkit.Load(source, configkit.Options[Document]{
 		Definition: documentDefinition(state),
 		Imports:    imports,
-		Profile:    options.Profile,
+		Overlay:    options.Overlay,
 		Overrides:  options.Overrides,
 	})
 }