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/migrations/20260609100000_uploaded_files/migration.sql

@@ -0,0 +1,19 @@
+-- CreateTable
+CREATE TABLE "uploaded_files" (
+    "id" TEXT NOT NULL,
+    "filename" TEXT NOT NULL,
+    "category" VARCHAR(32) NOT NULL,
+    "mime_type" VARCHAR(64) NOT NULL,
+    "size" INTEGER NOT NULL,
+    "url" VARCHAR(500) NOT NULL,
+    "uploaded_by" BIGINT,
+    "created_at" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "uploaded_files_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "uploaded_files_filename_key" ON "uploaded_files"("filename");
+
+-- CreateIndex
+CREATE INDEX "uploaded_files_category_idx" ON "uploaded_files"("category");