The pipeline's main select loop was reading from frameCh alongside the
SimpleTranscriber's collectAudio goroutine. Since Go channels deliver
each value to exactly one reader, the pipeline was randomly consuming
~50% of audio frames and discarding them, causing the transcriber to
receive fragmented audio and produce incomplete transcriptions.
Remove the `case <-frameCh:` from the pipeline loop so all frames are
exclusively consumed by the transcriber.
