Expand description
Per-vendor profile bundles per ADR-001.
Each vendor module owns its PREFIXES const, its EventExtensions
and (in later steps) CalendarExtensions types, plus owns_property
and parse/format helpers. Properties that match a vendor’s prefix but
aren’t yet typed land in the bundle’s unrecognized slot — promoting
them to typed fields later is intra-bundle and never crosses through
VEvent.unknown.