v1.32.1 — Self-update restart label fix

Fixed

• Self-update was always mislabelled as an "external stop signal (SIGTERM)" on the next boot (#2). The marker that tells the freshly-booted process "this restart was my own self-update" was never actually written: _do_selfupdate read the marker path off its local config variable — the docker-inspect dict (needed for the recreate), not the app Config object — so the write raised AttributeError, got swallowed by its best-effort try/except, and the error only ever printed inside the old container that was about to be deleted.

  Affected both the manual /selfupdate and the scheduled auto-self-update path, on every self-update since the marker was introduced in v1.26.2. Fixed by reading the path off self.config.selfupdate_marker_file (extracted into _write_selfupdate_marker). A self-update no longer prints the misleading "restarted after an external stop — Docksentry did not restart itself" line.

  Regression test added in scripts/test_selfupdate_marker.py — the previous test only covered the boot-side read logic, never the write, which is why this slipped through.