TMDB reports vote_average: 0 where no rating exists (#156). Normalise
it to None at the arr-meta edge, like non_empty does for "", and let
the Option flow through the daemon refresh and API add paths so the
nullable columns from #145 do their job.
movie_detail/series_detail fetch credits, videos and external ids in
one upstream request via append_to_response; cast is truncated to the
top 10 billed in the crate and a trailer is chosen by rule (official
YouTube trailer, any YouTube trailer, YouTube teaser, none).
movie_videos/series_videos serve #144's search-row chip from the
videos endpoint alone. Everything rides the existing 24h cache.