fix: change mock portal url to use .json extension for correct content-type

deploy/docker-compose.yml

@@ -14,7 +14,7 @@ services:
       # 향후 실제 AX Portal이 배포되면 아래 주소를 진짜 포털 주소로 변경하시기 바랍니다.
       # 예: - MCP_PORTAL_REGISTRY_URL=https://axhub.devjun.net/api/portal/registry
       # ====================================================================================
-      - MCP_PORTAL_REGISTRY_URL=http://portal-mock/api/portal/registry
+      - MCP_PORTAL_REGISTRY_URL=http://portal-mock/registry.json
     restart: always
     networks:
       - prd-dap-net
@@ -22,7 +22,7 @@ services:
   portal-mock:
     image: nginx:alpine
     volumes:
-      - ./portal-registry.json:/usr/share/nginx/html/api/portal/registry:ro
+      - ./portal-registry.json:/usr/share/nginx/html/registry.json:ro
     restart: always
     networks:
       - prd-dap-net