Add user membership and admin customer management APIs.

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

prisma/migrations/20260928160000_user_membership/migration.sql

@@ -0,0 +1,5 @@
+-- CreateEnum
+CREATE TYPE "Membership" AS ENUM ('regular', 'premium');
+
+-- AlterTable
+ALTER TABLE "User" ADD COLUMN "membership" "Membership" NOT NULL DEFAULT 'regular';