Add deployment service file and document system service setup

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

README.md

@@ -73,6 +73,17 @@ DELETE /api/tasks/:id      blocked if task has subtasks
 POST   /api/render-markdown   body: { text, mode? }   → { html }
 ```
 
+## Running as a system service
+
+`deployment/task-inventory.service` is a systemd unit file. To use it:
+
+1. Fill in `WorkingDirectory` with the path to the deployed app
+2. Create a dedicated user: `useradd -r task-inventory`
+3. Copy the unit file to `/etc/systemd/system/`
+4. `systemctl enable --now task-inventory`
+
+Packaging (Arch, Debian, etc.) is not set up yet.
+
 ## File map
 
 ```

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