feat(mobile): polish composer model/agent controls and selection overlay

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.

packages/ui/src/components/chat/ChatInput.tsx

@@ -4514,7 +4514,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                         {isMobile ? (
                             <>
                                 <div className="flex w-full items-center justify-between gap-x-1.5">
-                                    <div className="flex items-center gap-x-1.5">
+                                    <div className="composer-mobile-actions flex items-center gap-x-2 pl-1">
                                         <MobileSessionPanelTrigger
                                             footerIconButtonClass={footerIconButtonClass}
                                             iconSizeClass={iconSizeClass}
@@ -4539,7 +4539,7 @@ const ChatInputComponent: React.FC<ChatInputProps> = ({ onOpenSettings, scrollTo
                                         />
                                     </div>
                                     <div className="flex items-center min-w-0 gap-x-1 justify-end">
-                                        <div className="flex items-center gap-x-1 min-w-0 max-w-[60vw] flex-shrink">
+                                        <div className="flex items-center gap-x-2 min-w-0 max-w-[60vw] flex-shrink">
                                             <MemoMobileModelButton onOpenModel={() => handleOpenMobilePanel('model')} className="min-w-0 flex-shrink" />
                                             <MemoMobileAgentButton
                                                 onOpenAgentPanel={handleOpenAgentPanel}