💄 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 ? (

web/src/components/playground/CustomRequestEditor.js

@@ -1,12 +1,10 @@
 import React, { useState, useEffect } from 'react';
 import {
-  Card,
   TextArea,
   Typography,
   Button,
   Switch,
   Banner,
-  Tag,
 } from '@douyinfe/semi-ui';
 import {
   Code,
@@ -104,11 +102,6 @@ const CustomRequestEditor = ({
           <Typography.Text strong className="text-sm">
             自定义请求体模式
           </Typography.Text>
-          {customRequestMode && (
-            <Tag color="green" size="small" shape='circle'>
-              已启用
-            </Tag>
-          )}
         </div>
         <Switch
           checked={customRequestMode}
@@ -171,7 +164,7 @@ const CustomRequestEditor = ({
               onChange={handleValueChange}
               placeholder='{"model": "gpt-4o", "messages": [...], ...}'
               autosize={{ minRows: 8, maxRows: 20 }}
-              className={`!rounded-lg font-mono text-sm ${!isValid ? '!border-red-500' : ''}`}
+              className={`custom-request-textarea !rounded-lg font-mono text-sm ${!isValid ? '!border-red-500' : ''}`}
               style={{
                 fontFamily: 'Consolas, Monaco, "Courier New", monospace',
                 lineHeight: '1.5',