feat(cli): make /btw command non-blocking with parallel execution

- Add btwItem state management independent from pendingItem
- Add cancelBtw functionality to abort in-flight BTW API calls
- Allow /btw commands to execute concurrently with main responses
- Add isBtwCommand utility function
- Update BtwMessage UI with cleaner styling (remove spinner)
- Add tests for concurrent /btw execution scenarios
- Update layouts to render BTW messages in fixed bottom area

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/cli/src/ui/layouts/DefaultAppLayout.tsx

@@ -10,6 +10,7 @@ import { MainContent } from '../components/MainContent.js';
 import { DialogManager } from '../components/DialogManager.js';
 import { Composer } from '../components/Composer.js';
 import { ExitWarning } from '../components/ExitWarning.js';
+import { BtwMessage } from '../components/messages/BtwMessage.js';
 import { useUIState } from '../contexts/UIStateContext.js';
 import { useTerminalSize } from '../hooks/useTerminalSize.js';
 
@@ -21,6 +22,12 @@ export const DefaultAppLayout: React.FC = () => {
     <Box flexDirection="column" width={terminalWidth}>
       <MainContent />
 
+      {uiState.btwItem && (
+        <Box marginX={2} width={uiState.mainAreaWidth}>
+          <BtwMessage btw={uiState.btwItem.btw} />
+        </Box>
+      )}
+
       <Box flexDirection="column" ref={uiState.mainControlsRef}>
         {uiState.dialogsVisible ? (
           <Box marginX={2} flexDirection="column" width={uiState.mainAreaWidth}>