Add vocalist preset selector

docs/ARCHITECTURE.md

@@ -26,6 +26,7 @@ macOS App
 │   ├── Prompt Compiler
 │   ├── Genre & Style Catalog
 │   ├── Instrument Catalog
+│   ├── Vocalist Catalog
 │   ├── Arabic Pronunciation Processor
 │   ├── Project Versioning
 │   └── Validation
@@ -118,3 +119,10 @@ SwiftUI views. The Presentation layer may search, filter and toggle
 selections, while the catalog service owns stable ids, categories,
 optional regional metadata and search aliases. Selections are stored as
 existing `GenreStyle` values on the SongProject.
+
+## Vocalist Selector Boundary
+
+Vocalist presets are local structured data, separate from SwiftUI views.
+The catalog service supplies stable ids and preset metadata, while the
+Presentation layer searches and toggles the corresponding `Vocalist`
+values on the SongProject.