feat: add isPremium field to TelegramAccount

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/migrations/20260502000000_add_is_premium_to_telegram_account/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "telegram_accounts" ADD COLUMN "isPremium" BOOLEAN NOT NULL DEFAULT false;

prisma/schema.prisma

@@ -406,6 +406,7 @@ model TelegramAccount {
   isActive    Boolean   @default(true)
   authState   AuthState @default(PENDING)
   authCode    String?
+  isPremium   Boolean   @default(false)
   lastSeenAt  DateTime?
   createdAt   DateTime  @default(now())
   updatedAt   DateTime  @updatedAt