feat(webui): add webview container and isolate styles for VSCode integration

- Introduce WebviewContainer component for style isolation in VSCode webviews
- Rename CSS variables from --app-* to --qwen-app-* to prevent conflicts
- Add dedicated webview.css with isolated styles
- Update exports to include webview.css in package
- Modify all components to use new CSS variable names
- Update VSCode IDE companion to use new webview container
- Add style isolation to prevent conflicts with VSCode environment

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

Fixes webview UI issues in VSCode IDE Companion by providing proper style encapsulation.

packages/webui/src/components/WebviewContainer.tsx

@@ -0,0 +1,17 @@
+import type { PropsWithChildren } from 'react';
+import type React from 'react';
+
+interface WebviewContainerProps extends PropsWithChildren {
+  className?: string;
+}
+
+/**
+ * A container component that provides style isolation for VSCode webviews
+ * This component wraps content in a namespace to prevent style conflicts
+ */
+const WebviewContainer: React.FC<WebviewContainerProps> = ({
+  children,
+  className = '',
+}) => <div className={`qwen-webui-container ${className}`}>{children}</div>;
+
+export default WebviewContainer;