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/StatusRowContainer.tsx

@@ -46,8 +46,6 @@ export const StatusRowContainer: React.FC = React.memo(() => {
             wasAborted={wasAborted || working.wasAborted}
             abortActive={wasAborted || working.abortActive}
             retryInfo={working.retryInfo}
-            showAssistantStatus
-            showTodos={false}
             agentName={currentAgentName}
             modelName={modelDisplayName}
             providerId={activeModel?.providerId ?? null}