Integrate Streamdown and optimize chat layout

- Replace react-markdown with Streamdown for better streaming support
- Fix input box positioning with proper sidebar offset
- Optimize scrolling behavior with main container handling scroll
- Add max-width constraint for assistant messages
- Ensure proper spacing to prevent input box overlap

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/components/chat/index.tsx

@@ -174,7 +174,7 @@ const Chat: FC<IChatProps> = ({
       </div>
       {
         !isHideSendInput && (
-          <div className={cn(!feedbackDisabled && '!left-3.5 !right-3.5', 'absolute z-10 bottom-0 left-0 right-0')}>
+          <div className='fixed z-10 bottom-0 left-1/2 transform -translate-x-1/2 pc:ml-[122px] tablet:ml-[96px] mobile:ml-0 pc:w-[794px] tablet:w-[794px] max-w-full mobile:w-full px-3.5'>
             <div className='p-[5.5px] max-h-[150px] bg-white border-[1.5px] border-gray-200 rounded-xl overflow-y-auto'>
               {
                 visionConfig?.enabled && (

app/components/index.tsx

@@ -703,8 +703,7 @@ const Main: FC<IMainProps> = () => {
 
           {
             hasSetInputs && (
-              <div className='relative grow h-[200px] pc:w-[794px] max-w-full mobile:w-full pb-[120px] mx-auto mb-3.5 overflow-hidden'>
-                <div className='h-full overflow-y-auto' ref={chatListDomRef}>
+              <div className='relative grow pc:w-[794px] max-w-full mobile:w-full pb-[180px] mx-auto mb-3.5' ref={chatListDomRef}>
                 <Chat
                   chatList={chatList}
                   onSend={handleSend}
@@ -714,7 +713,6 @@ const Main: FC<IMainProps> = () => {
                   visionConfig={visionConfig}
                   fileConfig={fileConfig}
                 />
-                </div>
               </div>)
           }
         </div>