fix(ci): add SSH certificate for deploy authentication

Closes #38
Assisted-by: Claude:claude-sonnet-4-6

.github/workflows/ui.yml

@@ -103,9 +103,11 @@ jobs:
       - name: SSH deploy
         env:
           SSH_KEY: ${{ secrets.SSH_PRIVATE_KEY }}
+          SSH_CERT: ${{ secrets.SSH_CERTIFICATE }}
           SHA_TAG: ${{ needs.docker.outputs.sha_tag }}
         run: |
           echo "$SSH_KEY" > /tmp/deploy_key
+          echo "$SSH_CERT" > /tmp/deploy_key-cert.pub
           chmod 600 /tmp/deploy_key
           ssh -i /tmp/deploy_key \
             -p ${{ secrets.SSH_PORT }} \
@@ -118,4 +120,4 @@ jobs:
           docker rm   dashboard-ui 2>/dev/null || true
           docker run -d --name dashboard-ui --restart unless-stopped -p 80:80 $SHA_TAG
           EOF"
-          rm /tmp/deploy_key
+          rm /tmp/deploy_key /tmp/deploy_key-cert.pub