feat: refactor agent manager, media library, and player UX

- Split admin users page into player/tier-1/tier-2 tabs with affiliation labels and context-specific create dialogs

- Add media library with uploaded_files migration, list/delete unused files API, and admin nav route

- Enforce player username format (alphanumeric 3-32) on frontend and backend via shared package

- Improve admin dialog/panel styling; refine player parlay and match bet card kickoff display

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/shared/src/index.ts

@@ -119,6 +119,7 @@ export * from './betting-rules';
 export * from './locale';
 export * from './builtinPlayers';
 export * from './playerLocale';
+export * from './playerUsername';
 
 export interface ApiResponse<T = unknown> {
   success: boolean;