Show the video that was already arriving

The call wall asked the media plane who had a picture, at render time.
glimmer re-renders a component when a ratom it read has changed, and that
question read none — so the wall rendered once, with nobody on screen, and
was never told that anyone had appeared. Frames arrived, were handed to
Vidya, and painted into a node that had never been created.

So the pump publishes the feed list into a cell and the wall reads that.
Written only when the set actually changes: writing every frame would
rebuild every :image node sixty times a second around textures that were
fine where they were.

The row is always present now, so a tile appearing adds a child instead of
changing the shape of the tree around it — and its children are a seq
rather than a vector, because children splice and a vector is read as one
more element, which an empty one is not.

Also call joltmoq_init_logging, which was bound and never called. RUST_LOG
is the only thing that can see MoQ subscription and device open; the plane
was silent about all of it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>