feat(api): admin vocabulary + term management

GET/POST /api/admin/vocabularies and GET/POST /api/admin/vocabularies/{id}/terms;
reads gated on ViewInternal, writes on EditCatalogue; labels round-trip verified.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/api/src/lib.rs

@@ -2,6 +2,7 @@
 
 mod admin;
 mod admin_objects;
+mod admin_vocab;
 mod health;
 mod openapi;
 mod pagination;
@@ -43,6 +44,7 @@ pub fn build_app(state: AppState) -> Router {
         .merge(public::routes())
         .merge(admin::routes())
         .merge(admin_objects::routes())
+        .merge(admin_vocab::routes())
         .layer(session_layer)
         .with_state(state)
 }