Emby PremiereDate is the first air date for episodes/series and the
release date for movies. Request it again in Fields, emit it as
YYYY-MM-DD on search/browse/queue items, and document the conversation
prompt so Assist can answer airdate questions.
Potential breaking change: item JSON gains premiere_date versus the
1.0.11 slim shape. HA function parameter YAML is unchanged; re-paste
the DOCS.md system prompt.