💄 style(ui): hide scrollbars across chat interface and request editor

Hide y-axis scrollbars to provide a cleaner UI experience while maintaining
scroll functionality through mouse wheel and keyboard navigation.

Changes include:
- Hide scrollbars in CustomRequestEditor TextArea component
- Hide scrollbars in chat container and all related chat components
- Hide scrollbars in thinking content areas
- Add cross-browser compatibility for scrollbar hiding
- Maintain scroll functionality while improving visual aesthetics

Components affected:
- CustomRequestEditor.js: Added custom-request-textarea class
- index.css: Updated scrollbar styles for chat, thinking, and editor areas

The interface now provides a more streamlined appearance consistent with
modern UI design patterns while preserving all interactive capabilities.

web/src/components/playground/ChatArea.js

@@ -39,7 +39,7 @@ const ChatArea = ({
   return (
     <Card
       className="!rounded-2xl h-full"
-      bodyStyle={{ padding: 0, height: 'calc(100vh - 101px)', display: 'flex', flexDirection: 'column', overflow: 'hidden' }}
+      bodyStyle={{ padding: 0, height: 'calc(100vh - 108px)', display: 'flex', flexDirection: 'column', overflow: 'hidden' }}
     >
       {/* 聊天头部 */}
       {styleState.isMobile ? (