feat(cli): implement automatic theme switching based on terminal background (#17976)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/AppContainer.tsx

@@ -141,6 +141,7 @@ import {
 import { LoginWithGoogleRestartDialog } from './auth/LoginWithGoogleRestartDialog.js';
 import { NewAgentsChoice } from './components/NewAgentsNotification.js';
 import { isSlashCommand } from './utils/commandUtils.js';
+import { useTerminalTheme } from './hooks/useTerminalTheme.js';
 
 function isToolExecuting(pendingHistoryItems: HistoryItemWithoutId[]) {
   return pendingHistoryItems.some((item) => {
@@ -601,6 +602,9 @@ export const AppContainer = (props: AppContainerProps) => {
     initializationResult.themeError,
   );
 
+  // Poll for terminal background color changes to auto-switch theme
+  useTerminalTheme(handleThemeSelect, config);
+
   const {
     authState,
     setAuthState,