feat: add Proxmox LXC deployment files

- Add deploy/proxmox-lxc-setup.sh to configure the frontend inside a Debian/Ubuntu LXC.
- Add deploy/thermopro-frontend.service systemd unit.
- Add deploy/README.md with Proxmox CT creation, file transfer, setup, proxy, and update steps.
- Update frontend README.md to point to the deployment guide.

frontend/deploy/thermopro-frontend.service

@@ -0,0 +1,20 @@
+[Unit]
+Description=ThermoPro CYD Frontend
+After=network.target
+
+[Service]
+Type=simple
+User=thermopro
+Group=thermopro
+WorkingDirectory=/opt/thermopro-frontend
+Environment=CYD_BASE_URL=http://192.168.2.55
+Environment=POLL_INTERVAL=5
+Environment=DATABASE_PATH=/data/thermopro.db
+Environment=PYTHONDONTWRITEBYTECODE=1
+Environment=PYTHONUNBUFFERED=1
+ExecStart=/usr/bin/python3 /opt/thermopro-frontend/app.py
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target