stream_only / samples_only wont stream

Files with stream_only or samples_only in their collections can't be streamed. This is because the torrent file isn't available. Policy decision not to, at this point, create torrent files of the streamable parts of these items. So any items with stream_only or samples_only should
a) be filtered from collection results (or related items
b) show some kind of error if accessed directly.

Start with issue #90 and trace how collection or related-item results reach the streaming path for items marked stream_only or samples_only. Confirm the existing behavior for direct access and collection results, then ensure these items are either excluded from listings or produce an error when accessed directly.

Written by the indexing model from the issue text.