chore: scaffold backend venv, health check, systemd unit

deploy/quantumancy.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=Quantumancy web app
+After=network.target postgresql.service
+
+[Service]
+Type=simple
+WorkingDirectory=/root/quantumancy/backend
+EnvironmentFile=/root/quantumancy/.env
+ExecStart=/root/quantumancy/backend/venv/bin/uvicorn app.main:app --host 0.0.0.0 --port 7777
+Restart=on-failure
+RestartSec=3
+
+[Install]
+WantedBy=multi-user.target