The render-complete summary printed `<fileSize> · <time> · completed`
where `<time>` was the wall-clock render duration. Presented as a bare
middle value, users read it as the video length and compared it to
ffprobe, repeatedly reporting a "wrong duration".
Show the actual output video length (from the perf summary's
compositionDurationSeconds, which equals the rendered frame span) as the
primary figure and label the render time explicitly:
`<fileSize> · <videoLength> video · rendered in <renderTime>`.
png-sequence (directory) output has no single muxed video, so it shows a
frame count instead; when neither is known the summary falls back to
render time only. Docker renders run the producer in a child process
with no perf summary threaded back, so they show render time only rather
than a misleading number.
