feat(api): enum-typed visibility/data_type/kind + open-map fields in OpenAPI (#24 #29)

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

crates/api/src/admin_objects.rs

@@ -40,9 +40,10 @@ pub(crate) struct AdminObjectView {
     /// `YYYY-MM-DD` or null.
     pub recording_date: Option<String>,
     /// "draft" | "internal" | "public".
+    #[schema(value_type = domain::Visibility)]
     pub visibility: String,
     /// Flexible field values (key -> value).
-    #[schema(value_type = Object)]
+    #[schema(value_type = std::collections::HashMap<String, serde_json::Value>)]
     pub fields: serde_json::Value,
 }
 
@@ -162,7 +163,6 @@ pub(crate) struct ObjectCreateRequest {
     pub recorder: Option<String>,
     pub recording_date: Option<String>,
     /// "draft" | "internal" (public is rejected — publish via the visibility endpoint).
-    #[schema(value_type = String)]
     pub visibility: Visibility,
 }
 
@@ -360,8 +360,10 @@ pub(crate) async fn delete_object(
 pub(crate) struct FieldDefinitionView {
     pub key: String,
     /// "text" | "localized_text" | "integer" | "date" | "boolean" | "term" | "authority".
+    #[schema(value_type = domain::DataType)]
     pub data_type: String,
     pub vocabulary_id: Option<String>,
+    #[schema(value_type = Option<domain::AuthorityKind>)]
     pub authority_kind: Option<String>,
     pub required: bool,
     pub group: Option<String>,