fix(classification): consistent type on public pack + guest serializers

Commit notes

Extend the displayType treatment to the remaining UI surfaces that show a sample "Type" so it stays consistent everywhere, not just the library grid:

- Public creator pack page (creators.ts + /u/[slug]/pack/[packSlug]) rendered raw `drumType` (CLAP instrument), which is null until CLAP runs. Now it surfaces and renders `displayType` (instrument, else Essentia's structural sample type), so it is populated for any analyzed sample. - Pack-generator (guest samples) serializer now exposes sampleType/displayType; guest samples have no CLAP instrument, so it derives from the Essentia structural type / loop detection.

Co-Authored-By: Claude Opus 4.8 <[email redacted]> Claude-Session: [private session redacted]