Redesign the mobile composer model and agent buttons as borderless, full-bleed
labels that hug their content, truncate with an ellipsis when space is tight,
and show the provider logo inline before the model name. Tighten the footer
action buttons (sessions / attach / auto-accept) so they sit close together,
with a small left inset on the group. In the mobile model selection overlay,
make the thinking-variant control text-only with a chevron, vertically center
the variant and favorite controls in each row, and place the provider logo
inline with the model name.