Update refserver deploy workflow for systemd target

[aditya-damerla128]

Summary

• replace the reference-server deploy's Appleboy SCP/SSH actions with direct SSH setup, rsync upload, and ssh remote execution
• remove the custom SSH port and PM2 restart path from the reference-server deploy
• wire the deployed refserver runtime to PORT=8000 and make the systemd restart command configurable

Notes

• Demo-site deployment is intentionally unchanged; it still needs a later follow-up for the new refserver URL.
• Aaron still needs to confirm the runner label, deploy host/path, and whether the restart command should use passwordless sudo or user-level systemd.

Validation

• python3 -c "import yaml; yaml.safe_load(open('.github/workflows/deploy-reference-server.yml')); print('yaml ok')"
• rg -n "appleboy|pm2|port: 2061" .github/workflows/deploy-reference-server.yml
• git diff --check -- .github/workflows/deploy-reference-server.yml
• act -n -W .github/workflows/deploy-reference-server.yml

Fixes #214