Adds the 3.6 MB take-3 walkthrough mp4 that README already references
via a poster image, and replaces the "coming in a follow-up commit"
placeholder line with a real link (poster now click-through to the
video, caption points at the same file).
Path: examples/desktop/docs/demo-shots/showcase-2026-07-18/
demo-walkthrough.mp4
No source or config changes; the shell tree from a3ca492a is byte-
identical to what it was, this commit just fills in the recording
slot the previous docs commit deferred.
ZiyaZhang
69687895fa