Keep the phone shell on a phone held sideways

A phone in landscape is 844 to 932 px wide, past md, so it got the
desktop rail and top bar: a sliver of content and no thumb-reachable
navigation. Two variants now decide the shell: shell-desktop from md up
except on a touch screen at most 520 px tall, shell-mobile otherwise.
The sidebar, top bar, bottom nav, the main column's bottom clearance,
the Coach button, the selection bar and the two full-height Coach pages
all key on them instead of a bare md.

src/components/data-list/selection-action-bar.tsx

@@ -82,7 +82,7 @@ export function SelectionActionBar({
       // an `sm:` drop sat the bar behind the still-visible nav 640-767px.
       // z-30 keeps the bar above page content without needing to beat the
       // (now-cleared) nav's z-50.
-      className="bg-card border-border sticky bottom-[calc(env(safe-area-inset-bottom,0px)+5rem)] z-30 mt-2 flex items-center justify-between gap-2 rounded-lg border p-2 shadow-lg md:bottom-4"
+      className="bg-card border-border sticky bottom-[calc(env(safe-area-inset-bottom,0px)+5rem)] z-30 mt-2 flex items-center justify-between gap-2 rounded-lg border p-2 shadow-lg shell-desktop:bottom-4"
     >
       <div className="flex items-center gap-1">
         <Button