fix(migration): update systemd service file during v3→v4 migration

Critical fixes for v3→v4 migration:

1. install.sh: Auto-update systemd service file during migration
   - Calls 'nupst service enable' before restarting service
   - Only when migrating from v3 (OLD_NODE_INSTALL=1)
   - Ensures service file has correct v4 paths

2. ts/systemd.ts: Fix hardcoded v3 paths in service template
   - ExecStart: /opt/nupst/bin/nupst daemon-start (v3, broken)
              → /usr/local/bin/nupst service start-daemon (v4, correct)
   - Description: Updated to 'Deno-powered UPS Monitoring Tool'
   - Added RestartSec=10 (prevent rapid restart loops)
   - Removed NODE_ENV=production (not needed for Deno)
   - WorkingDirectory: /tmp → /opt/nupst

Without these fixes:
- Service fails to start after migration
- Service file points to non-existent /opt/nupst/bin/nupst
- Users must manually run 'nupst service enable'

Discovered via Docker migration testing in test/manualdocker/

install.sh

@@ -340,6 +340,14 @@ fi
 
 echo ""
 
+# Update systemd service file if migrating from v3
+if [ $SERVICE_WAS_RUNNING -eq 1 ] && [ $OLD_NODE_INSTALL -eq 1 ]; then
+  echo "Updating systemd service file for v4..."
+  $BINARY_PATH service enable > /dev/null 2>&1
+  echo "Service file updated."
+  echo ""
+fi
+
 # Restart service if it was running before update
 if [ $SERVICE_WAS_RUNNING -eq 1 ]; then
   echo "Restarting NUPST service..."