Add vocalist preset selector

docs/PRODUCT.md

@@ -36,6 +36,8 @@ and writing engine, then prepares final lyrics and style instructions.
 -   Song structure supports Manual and Auto modes.
 -   BPM, key/scale and maqam support Manual and Auto modes.
 -   Multiple vocalists/voices can exist in one song.
+-   Vocalists can be selected from a local catalog of voice roles and
+    presets using checkbox multi-select.
 -   User controls vocal gender/type, rap/singing mode, delivery and
     section-specific performance.
 -   Multiple languages and dialects can be used in one song.
@@ -85,6 +87,13 @@ region/origin where useful, and select or deselect multiple entries with
 checkboxes. Catalog data is structured and separate from SwiftUI views;
 it does not require an external API.
 
+## Vocalist Selector
+
+The application provides a local catalog of vocalist roles and voice
+presets. Users can search, browse by category and select or deselect
+multiple vocalists with checkboxes. Each preset supplies a role label,
+voice type, gender selection and performance style for the Song Project.
+
 ## Project Management
 
 Every song is stored as a project. Important changes can create versions