refactor(backend): Scalar UI 제거 및 API 문서 포털용 CORS 설정

- /docs 라우트(Scalar UI) 제거 → docs.caadiq.co.kr에서 통합 제공
- /docs/json 엔드포인트에 CORS 헤더 추가

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

backend/src/app.js

@@ -4,7 +4,6 @@ import { fileURLToPath } from 'url';
 import Fastify from 'fastify';
 import fastifyStatic from '@fastify/static';
 import fastifySwagger from '@fastify/swagger';
-import scalarApiReference from '@scalar/fastify-api-reference';
 import multipart from '@fastify/multipart';
 import config from './config/index.js';
 import * as schemas from './schemas/index.js';
@@ -92,19 +91,10 @@ export async function buildApp(opts = {}) {
     },
   });
 
-  // Scalar API Reference UI
-  await fastify.register(scalarApiReference, {
-    routePrefix: '/docs',
-    configuration: {
-      theme: 'purple',
-      spec: {
-        url: '/docs/json',
-      },
-    },
-  });
-
-  // OpenAPI JSON 엔드포인트
-  fastify.get('/docs/json', { schema: { hide: true } }, async () => {
+  // OpenAPI JSON 엔드포인트 (CORS 허용 - API 문서 포털용)
+  fastify.get('/docs/json', { schema: { hide: true } }, async (request, reply) => {
+    reply.header('Access-Control-Allow-Origin', 'https://docs.caadiq.co.kr');
+    reply.header('Access-Control-Allow-Methods', 'GET');
     return fastify.swagger();
   });