Add deployment service file and document system service setup

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

deployment/task-inventory.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Task Inventory
+#RequiresMountsFor=...
+After=network.target
+
+[Service]
+User=task-inventory
+Group=task-inventory
+Type=simple
+ExecStart=node server.mjs
+WorkingDirectory= MUST BE FILLED IN
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target