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/utils/commandUtils.ts

@@ -62,6 +62,21 @@ export const isSlashCommand = (query: string): boolean => {
   return true;
 };
 
+/**
+ * Checks if a query is a /btw side-question invocation.
+ * Accepts both "/btw" and "?btw" prefixes.
+ */
+export const isBtwCommand = (query: string): boolean => {
+  const trimmed = query.trim();
+  if (!trimmed) {
+    return false;
+  }
+
+  const normalized = trimmed.startsWith('?') ? `/${trimmed.slice(1)}` : trimmed;
+
+  return /^\/btw(?:\s|$)/.test(normalized);
+};
+
 const debugLogger = createDebugLogger('COMMAND_UTILS');
 
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