web: a recording of the theme picker, and the tour step for it

The landing page's feature tour is scripted recordings -- driver scripts
against `slosh --script` on a virtual clock, re-rendered by `make` so a UI
change can never leave a stale demo -- and the picker is exactly the kind of
thing that does not survive being described. "Moving the selection applies the
theme" is a sentence; twenty-six seconds of a session changing colour under a
list is the claim itself.

demos/themes.py: a sidebar session with two tabs and a build pane that says it
is busy (so the spinner is in shot, turning in whatever colour the theme being
tried says it should), `cat config.kdl` showing a config that names a theme and
holds no colours at all, then C-a t -- the list, two themes worn rather than
swatched, `pho` typed to narrow, C-s writing the one line, a second `cat`
proving it wrote that line and nothing else, and finally a browse that ends in
Escape, which puts back what was worn.

Two rules the demo had to obey, both now in PLAN.md beside the other lessons:
only dark themes, because cells slosh does not paint keep the terminal's own
background and the cast header fixes that once -- `paper` would look broken in
the player and fine in a light terminal; and nothing on screen may carry this
machine, so the themes are copied next to the temp config rather than pointed
at with `theme_dir`, leaving a `cat` frame that reads as a name and a
directory nobody has to have.

The step slots after "make it yours, live", which is where a reader has just
been shown a config being edited by hand and is best placed to notice that a
theme is one word of it. Casts are built at publish time, so build-site picks
the new one up with no wiring.

0 files changed, 0 insertions, 0 deletions