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>

apps/api/prisma/schema.prisma

@@ -595,6 +595,22 @@ model I18nMessage {
   @@map("i18n_messages")
 }
 
+// ============ Media / File Uploads ============
+
+model UploadedFile {
+  id         String   @id @default(uuid())
+  filename   String   @unique
+  category   String   @db.VarChar(32)
+  mimeType   String   @map("mime_type") @db.VarChar(64)
+  size       Int
+  url        String   @db.VarChar(500)
+  uploadedBy BigInt?  @map("uploaded_by")
+  createdAt  DateTime @default(now()) @map("created_at")
+
+  @@index([category])
+  @@map("uploaded_files")
+}
+
 // ============ System Config & Audit ============
 
 model SystemConfig {