Every item_updated WebSocket event and every history/queue list response
was serializing the full ItemDTO including fields the UI never reads.
Add ItemDTO.serialize_for_list() which excludes: options,
template_chapter, temp_dir, total_bytes, total_bytes_estimate,
tmpfilename, archive_id. The global Encoder now uses serialize_for_list()
for all list/event contexts; the full serialize() remains available for
detail endpoints (GET /api/history/{id}).
Mark the excluded fields optional in the TypeScript StoreItem type.
