feat: add Queue-based server provisioning with security fixes

- Add Cloudflare Queue for async server provisioning
  - Producer: callback-handler.ts sends to queue
  - Consumer: provision-consumer.ts processes orders
  - DLQ: provision-dlq.ts handles failed orders with refund

- Security improvements (from code review):
  - Store password hash instead of plaintext (SHA-256)
  - Exclude root_password from logs
  - Add retryable flag to prevent duplicate instance creation
  - Atomic balance deduction with db.batch()
  - Race condition prevention with UPDATE...WHERE status='pending'
  - Auto-refund on DLQ processing

- Validation improvements:
  - OS image whitelist validation
  - Session required fields validation
  - Queue handler refactoring

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/index.ts

@@ -1,4 +1,4 @@
-import { Env, EmailMessage } from './types';
+import { Env, EmailMessage, ProvisionMessage } from './types';
 import { sendMessage, setWebhook, getWebhookInfo } from './telegram';
 import { handleWebhook } from './routes/webhook';
 import { handleApiRequest } from './routes/api';
@@ -6,6 +6,8 @@ import { handleHealthCheck } from './routes/health';
 import { parseBankSMS } from './services/bank-sms-parser';
 import { matchPendingDeposit } from './services/deposit-matcher';
 import { reconcileDeposits, formatReconciliationReport } from './utils/reconciliation';
+import { handleProvisionQueue } from './queue/provision-consumer';
+import { handleProvisionDLQ } from './queue/provision-dlq';
 
 export default {
   // HTTP 요청 핸들러
@@ -279,4 +281,19 @@ Documentation: https://github.com/your-repo
       // 정합성 검증 실패가 전체 Cron을 중단시키지 않도록 에러를 catch만 하고 계속 진행
     }
   },
+
+  // Queue 핸들러 (서버 프로비저닝)
+  async queue(batch: MessageBatch<ProvisionMessage>, env: Env): Promise<void> {
+    const QUEUE_HANDLERS: Record<string, (batch: MessageBatch<ProvisionMessage>, env: Env) => Promise<void>> = {
+      'server-provision-queue': handleProvisionQueue,
+      'provision-dlq': handleProvisionDLQ,
+    };
+
+    const handler = QUEUE_HANDLERS[batch.queue];
+    if (handler) {
+      return handler(batch, env);
+    }
+
+    console.error(`[Queue] Unknown queue: ${batch.queue}`);
+  },
 };