New report fields: envelope_from, discovery_method, generator

RFC 9990 (the DMARCbis aggregate-reporting RFC) adds a handful of optional fields to the report XML this tool already ingests and parses:

• generator — the name/version of the software that produced the report, in report_metadata.
• discovery_method — whether the reporting receiver used psl or treewalk to find your organizational domain, in policy_published.
• envelope_from / envelope_to — the SMTP envelope sender/recipient domains for that record, alongside the existing header_from.

All of these are optional and absent on every classic-era report — which is still the normal case for years to come, since most reporting infrastructure hasn't updated yet. This tool captures whichever of them a report actually includes and stores them (reports.generator/discovery_method, report_records.envelope_from/envelope_to), but doesn't yet surface them anywhere in the dashboard — that's a possible future addition once there's enough real-world data flowing in to make a dedicated view worthwhile.