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.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=cTrader MS_SimpleExport daily market-data export
+# The export writes to the NFS-mounted data dir and logs into cTrader over the network.
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+User=brummel
+SupplementaryGroups=docker
+ExecStart=/home/brummel/dev/cTrader/scripts/cron-export.sh
+# A full run is ~15-20 min; allow generous head-room for gap backfills.
+TimeoutStartSec=2h