Adds a gear button to the nav that opens a settings modal with:
- Export: GET /api/export returns all instances as a JSON backup file
with a Content-Disposition attachment header
- Import: POST /api/import validates and bulk-replaces all instances;
client uses FileReader to POST the parsed JSON, with a confirm dialog
before destructive replace
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Production images continue to display the semver (v1.x.x). Dev images
built by CI now receive BUILD_VERSION=dev-<7-char-sha> via a Docker ARG,
and app.js skips the v prefix for non-semver strings.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
