feat(scrollToBottom)：聊天页新增滚动到底部按钮

frontend/src/app/workspace/chats/[thread_id]/page.tsx

@@ -333,8 +333,7 @@ export default function ChatPage() {
                 )}
               >
                 <div className="flex size-full justify-center">
-                    {!showWelcomeStyle &&
-                      <MessageList
+                    <MessageList
                       className={cn(
                         "size-full",
                         (!showWelcomeStyle || hasSubmitted) && "pt-[58px]",
@@ -347,8 +346,10 @@ export default function ChatPage() {
                           : thread.messages.slice(historyCutoff)
                       }
                       paddingBottom={todoListCollapsed ? 160 : 280}
+                      // !showWelcomeStyle || hasSubmitted
+                      showScrollToBottomButton={!showWelcomeStyle}
+                      scrollButtonClassName="bottom-[112px]"
                     />
-                    }
                 </div>
               </main>
             </div>

frontend/src/components/ai-elements/conversation.tsx

@@ -84,7 +84,7 @@ export const ConversationScrollButton = ({
     !isAtBottom && (
       <Button
         className={cn(
-          "absolute bottom-4 left-[50%] translate-x-[-50%] rounded-full",
+          "absolute bottom-3 left-1/2 -translate-x-1/2 rounded-full",
           className,
         )}
         onClick={handleScrollToBottom}

frontend/src/components/workspace/messages/message-list.tsx

@@ -4,6 +4,7 @@ import type { UseStream } from "@langchain/langgraph-sdk/react";
 import {
   Conversation,
   ConversationContent,
+  ConversationScrollButton,
 } from "@/components/ai-elements/conversation";
 import { useI18n } from "@/core/i18n/hooks";
 import {
@@ -37,6 +38,8 @@ export function MessageList({
   messagesOverride,
   suppressThreadLoading = false,
   paddingBottom = 160,
+  showScrollToBottomButton = false,
+  scrollButtonClassName,
 }: {
   className?: string;
   threadId?: string;
@@ -45,6 +48,8 @@ export function MessageList({
   messagesOverride?: Message[];
   suppressThreadLoading?: boolean;
   paddingBottom?: number;
+  showScrollToBottomButton?: boolean;
+  scrollButtonClassName?: string;
 }) {
   const { t } = useI18n();
   const rehypePlugins = useRehypeSplitWordsIntoSpans(thread.isLoading);
@@ -205,9 +210,19 @@ export function MessageList({
             />
           );
         })}
-        {thread.isLoading && <StreamingIndicator className="my-4" />}
+        {thread.isLoading && messages.length > 0 && <StreamingIndicator className="my-4" />}
         <div style={{ height: `${paddingBottom}px` }} />
       </ConversationContent>
+      {/* showScrollToBottomButton */}
+      { showScrollToBottomButton && (
+        <ConversationScrollButton
+          className={cn(
+            "z-20 rounded-full border bg-white/90 shadow-sm backdrop-blur-sm",
+            scrollButtonClassName,
+          )}
+          title="滚动到底部"
+        />
+      )}
     </Conversation>
   );
 }