The desktop build break shipped because nothing in CI runs the
apps/desktop production build. typecheck only runs `tsc`, which does
not exercise Vite/Rolldown module resolution, so an unresolvable
package export (the @assistant-ui/tap "./react-shim" split) sailed
through green checks and only failed when users built from source on
install/update.
Add a desktop-build job that runs `npm run build` (tsc -b + vite build
+ assert-dist-built) for apps/desktop. This closes the gap so the same
class of break fails in CI instead of on every user's machine.
30377e108c