[fix] CI에 pnpm 버전 명시 (packageManager 필드 없어 자동 감지 실패)

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

Author: junh0328

.github/workflows/ci.yml

@@ -13,6 +13,8 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
+        with:
+          version: 9
 
       - uses: actions/setup-node@v4
         with: