feat(studio/robot-authors): category filter + display_name & category columns

- searchable CategoryPicker (Popover+Command) reusable across studio pages,
  plus useCategoryOptions hook (shared tree query + id→name resolver)
- filter bar with category + status filters and a reset action
- new columns: account (avatar + display_name + uid), category name; persona
  demoted to a secondary column; display_name/category surfaced in detail sheet

src/api/types.ts

@@ -145,6 +145,9 @@ export interface StudioRobotAuthor {
   kind: 'studio_robot_author'
   id: string
   user_uid: string
+  /** Bound robot account's public name (index listing only). */
+  display_name?: string | null
+  avatar?: string | null
   category_id: string
   subtopic_id: string | null
   persona: string | null