Updated from version 8.17.3 to the latest stable release 9.1.5 (released October 06, 2025).
Changes:
- Update ELASTIC_VERSION in Dockerfile to 9.1.5
- Update version reference in README.md to 9.1.5
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>