Folded attachment types now recorded and surfaced in debug output

The message-folding pass (still gated behind tengu_chair_sermon, default off), which maps user-turn content through a folding transform before merging it into the prior user message, now also records which attachment types were folded via a new foldedAttachmentTypes array attached to the resulting assembled api_system/user message.

A separate debug/summary formatter now reads this foldedAttachmentTypes field and prints it as a tagged line (e.g. index=type1+type2) when present.