Which stored preference Ctrl+S toggles, and how the footer names it.
The selector is reused for pickers that choose something other than the
main agent model (for example the /auto classifier), where persisting
[models].default would silently retarget the model the agent itself runs
on. Each caller supplies the scope whose [models] key its Ctrl+S owns, or
None to disable Ctrl+S entirely (see ModelSelectorScreen.__init__).
Nothing ties load, save, and clear to a single [models] key — that
they agree is a property of how each instance is built, so define scopes as
module-level constants next to each other rather than assembling them at a
call site.
