Add daily 03:30 export schedule (systemd timer)

This host has no cron daemon (it is systemd-based), so schedule export-runner.sh via a
systemd timer rather than cron. cron-export.sh wraps the run with a sane PATH, flock
serialisation (no overlapping runs), and per-run logs under runtime/logs/. The timer is
Persistent, so a 03:30 run missed because the machine was asleep/off is caught up on the
next boot -- which plain cron does not do.

- scripts/cron-export.sh: scheduled-run wrapper.
- deploy/systemd/ctrader-export.{service,timer}: the units (install: sudo cp into
  /etc/systemd/system/ then enable -- see deploy/systemd/README.md).

deploy/systemd/ctrader-export.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Run the cTrader market-data export daily at 03:30
+
+[Timer]
+OnCalendar=*-*-* 03:30:00
+# Catch up a missed run (e.g. the machine was asleep/off at 03:30) on next boot.
+Persistent=true
+Unit=ctrader-export.service
+
+[Install]
+WantedBy=timers.target