[AC-3505] fix: add root element to full screen component for modal (#329

)

## Changes

- Fixed a crash when opening a modal in the full-screen widget (root
element for React portal not found).

ticket: [AC-3505]

[AC-3505]:
https://sendbird.atlassian.net/browse/AC-3505?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

src/components/widget/WidgetWindowFullScreen.tsx

@@ -0,0 +1,23 @@
+import Chat from './Chat';
+import { ChatAiWidgetProps } from './ChatAiWidget';
+import ProviderContainer from './ProviderContainer';
+import { elementIds } from '../../const';
+
+/**
+ * NOTE: External purpose only.
+ * Do not use this component directly. Use Chat instead for internal use.
+ */
+function WidgetWindowFullScreen(props: ChatAiWidgetProps) {
+  return (
+    <ProviderContainer {...props}>
+      <div
+        id={elementIds.widgetWindow}
+        style={{ position: 'fixed', left: 0, top: 0, width: '100%', height: '100%', transform: 'scale(1)' }}
+      >
+        <Chat />
+      </div>
+    </ProviderContainer>
+  );
+}
+
+export default WidgetWindowFullScreen;

src/index.ts

@@ -1,6 +1,6 @@
 export { default as ChatAiWidget } from './components/widget/ChatAiWidget';
 export { type ProviderContainerProps as ChatAiWidgetConfigs } from './components/widget/ProviderContainer';
-export { default as ChatWindow } from './components/widget/WidgetWindowExternal';
+export { default as ChatWindow } from './components/widget/WidgetWindowFullScreen';
 export { widgetServiceName } from './const';
 export { clearWidgetSessionCache, clearCache } from './libs/storage/widgetSessionCache';