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/README.md

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+# Scheduled export (systemd timer)
+
+Runs `scripts/export-runner.sh` once a day at **03:30** via a systemd timer (this host
+has no cron daemon; the timer is native and, unlike cron, catches up a missed run with
+`Persistent=true` if the machine was asleep/off at 03:30).
+
+`ctrader-export.service` runs `scripts/cron-export.sh` as user `brummel` (a wrapper that
+sets a sane PATH, serialises with `flock`, and logs into `runtime/logs/`).
+
+## Install (one-time, needs sudo)
+
+```bash
+sudo cp deploy/systemd/ctrader-export.service deploy/systemd/ctrader-export.timer \
+        /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable --now ctrader-export.timer
+```
+
+## Verify / operate
+
+```bash
+systemctl list-timers ctrader-export.timer   # next/last fire time
+systemctl status ctrader-export.service      # last run result
+journalctl -u ctrader-export.service         # service-level logs
+ls -t runtime/logs/                          # per-run export logs
+sudo systemctl start ctrader-export.service  # run once now, on demand
+sudo systemctl disable --now ctrader-export.timer  # stop scheduling
+```
+
+Paths in the unit files are absolute (`/home/brummel/dev/cTrader`). If the repo moves,
+update `ExecStart` in `ctrader-export.service` and re-run the install steps.

deploy/systemd/ctrader-export.service

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+[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

deploy/systemd/ctrader-export.timer

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+[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

scripts/cron-export.sh

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+#!/usr/bin/env bash
+#
+# Wrapper for scheduled (systemd timer) runs of export-runner.sh.
+# Sets a sane PATH (schedulers run with a minimal environment), serialises runs with
+# flock so a slow run never overlaps the next tick, and logs each run under
+# runtime/logs/ (gitignored).
+set -uo pipefail
+
+export PATH="/usr/local/bin:/usr/bin:/bin"
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+LOG_DIR="$REPO_ROOT/runtime/logs"
+mkdir -p "$LOG_DIR"
+LOG="$LOG_DIR/export-$(date +%Y%m%d-%H%M%S).log"
+
+# Serialise: if a previous run is still going, skip this tick instead of piling up.
+exec 9>"$LOG_DIR/.lock"
+if ! flock -n 9; then
+    echo "$(date): another export run is still in progress — skipping this tick" >> "$LOG"
+    exit 0
+fi
+
+{
+    echo "=== scheduled export run: $(date) ==="
+    "$REPO_ROOT/scripts/export-runner.sh"
+    echo "=== exit $? at $(date) ==="
+} >> "$LOG" 2>&1
+
+# Keep the log dir tidy: drop runs older than 30 days.
+find "$LOG_DIR" -name 'export-*.log' -mtime +30 -delete 2>/dev/null || true