refactor(chat): split the composer status bar from the assistant status chip

The composer rendered a second StatusRow instance carrying the
pending-changes bar and the todos dropdown, so every restyle of the
floating assistant-status chip (glass, placement, sizing) silently
restyled the composer bar and its dropdown too — for the fourth time.

StatusRow is now only the floating chip above the composer; the
composer's own bar is a new ComposerStatusBar with the pre-glass layout,
its own container name, and its own container-query classes (the
anti-overlap rules that hide the long active todo under 38rem and the
changed-files label under 30rem moved with it — losing them during the
split let the two dropdown triggers overlap on mobile). The two
components share no markup and no CSS hooks anymore.

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

@@ -107,7 +107,7 @@ export const PendingChangesBar: React.FC = React.memo(() => {
             >
                 <Icon name="file-edit" className="h-3.5 w-3.5 flex-shrink-0 text-[var(--status-warning)]" />
                 <span className="min-w-0 typography-ui-label text-foreground flex-shrink-0">{labelHead}</span>
-                <span className="status-row__changed-label min-w-0 typography-ui-label text-foreground truncate">
+                <span className="composer-status-bar__changed-label min-w-0 typography-ui-label text-foreground truncate">
                     {t('chat.pendingChanges.changedInWorkspace')}
                 </span>
                 <span className="text-[0.75rem] tabular-nums inline-flex items-baseline gap-1 flex-shrink-0">