### Added
- Extracted `load_reverse_dns_map()` utility function in `utils.py` for loading the reverse DNS map independently of individual IP lookups.
- SIGHUP reload now re-downloads/reloads the reverse DNS map, so changes take effect without restarting.
- Add premade OpenSearch index patterns, visualizations, and dashboards
### Changed
- When `index_prefix_domain_map` is configured, SMTP TLS reports for domains not in the map are now silently dropped instead of being output. Unlike DMARC, TLS-RPT has no DNS authorization records, so this filtering prevents processing reports for unrelated domains.
- Bump OpenSearch support to `< 4`
### Fixed
- Fixed `get_index_prefix` using wrong key (`domain` instead of `policy_domain`) for SMTP TLS reports, which prevented domain map matching from working for TLS reports.
- Domain matching in `get_index_prefix` now lowercases the domain for case-insensitive comparison.
