debug: SSH 키 형식 확인 스텝 추가

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

.github/workflows/deploy.yml

@@ -24,6 +24,15 @@ jobs:
       - name: Build
         run: npm run build
 
+      - name: Debug SSH key
+        run: |
+          echo "=== key line count ==="
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" | wc -l
+          echo "=== first line ==="
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" | head -1
+          echo "=== last line ==="
+          echo "${{ secrets.SSH_PRIVATE_KEY }}" | tail -1
+
       - name: Deploy via SCP
         run: |
           mkdir -p ~/.ssh