fix: keep the welcome composer at the bottom

src/pages/Chat/CodingChatBody.tsx

@@ -7,14 +7,15 @@ export function CodingChatBody({ welcome, hidden, bubble, children }: {
   const ref = useRef<HTMLDivElement>(null);
   useLayoutEffect(() => {
     const body = ref.current;
-    if (!body || !welcome || hidden || !bubble) return;
+    const content = body?.querySelector<HTMLElement>('.classroom-chat-view');
+    if (!body || !content || !welcome || hidden || !bubble) return;
     const update = () => {
-      const area = body.getBoundingClientRect();
+      const area = content.getBoundingClientRect();
       const message = bubble.getBoundingClientRect();
       const overlaps = message.height > 0 && message.right > area.left && message.left < area.right && message.bottom > area.top;
       // Wide workspaces put the welcome beside the teachers. Compact ones flow below them.
-      body.style.paddingRight = overlaps && area.width >= 1050 ? `${Math.ceil(area.right - message.left + 24)}px` : '';
-      body.style.paddingTop = overlaps && area.width < 1050 ? `${Math.ceil(message.bottom - area.top + 24)}px` : '';
+      content.style.paddingRight = overlaps && area.width >= 1050 ? `${Math.ceil(area.right - message.left + 24)}px` : '';
+      content.style.paddingTop = overlaps && area.width < 1050 ? `${Math.ceil(message.bottom - area.top + 24)}px` : '';
     };
     update();
     const observer = typeof ResizeObserver === 'undefined' ? null : new ResizeObserver(update);
@@ -22,7 +23,7 @@ export function CodingChatBody({ welcome, hidden, bubble, children }: {
     window.addEventListener('resize', update);
     return () => {
       observer?.disconnect(); window.removeEventListener('resize', update);
-      body.style.paddingRight = ''; body.style.paddingTop = '';
+      content.style.paddingRight = ''; content.style.paddingTop = '';
     };
   }, [welcome, hidden, bubble]);
   return <div ref={ref} className="coding-chat-body" data-welcome={welcome} hidden={hidden}>{children}</div>;

src/pages/Chat/CodingChatPanel.tsx

@@ -835,7 +835,7 @@ export function CodingChatPanel({
           </div>
         )}
 
-        {showWelcome ? <CodingStartHeading /> : targetConversationId
+        {showWelcome ? <><CodingStartHeading /><CommunityInvitation /></> : targetConversationId
           ? (
             <CodingConversationTimeline
               key={targetConversationId}
@@ -965,7 +965,6 @@ export function CodingChatPanel({
           }}
         />}
         </div>
-        {showWelcome && <CommunityInvitation />}
         </CodingChatBody>
       </div>