docs: add persistent services section to SERVER.md

Documents tmux, user systemd, and pm2 options for running
long-lived processes. Notes lingering requirement for systemd.

docs/server-AGENTS.md

@@ -102,6 +102,50 @@ Other agents may have similar sandbox settings - check their docs if nix command
 - Fork-bomb or stress test (watchdogs will kill you)
 - Store secrets in plain files (use env vars)
 
+## Running Persistent Services
+
+Three options for keeping code running:
+
+### 1. tmux/screen (simplest)
+```bash
+tmux new -s mybot
+python bot.py
+# Ctrl-b d to detach, tmux attach -t mybot to reconnect
+```
+
+### 2. User systemd services
+```bash
+# Create service file
+mkdir -p ~/.config/systemd/user
+cat > ~/.config/systemd/user/mybot.service << 'EOF'
+[Unit]
+Description=My bot
+
+[Service]
+ExecStart=/home/YOURUSER/.bun/bin/bun run /home/YOURUSER/mybot/index.js
+Restart=on-failure
+RestartSec=5
+
+[Install]
+WantedBy=default.target
+EOF
+
+# Enable and start
+systemctl --user daemon-reload
+systemctl --user enable --now mybot
+systemctl --user status mybot
+systemctl --user logs -f mybot
+```
+
+**Note:** User services stop when you log out unless lingering is enabled (ask admin).
+
+### 3. Process managers (pm2, etc.)
+```bash
+bun install -g pm2
+pm2 start bot.js --name mybot
+pm2 save
+```
+
 ## Getting Help
 
 ```bash