feat(FN-5151): complete Step 1 — align MessageComposer cap

Fusion-Task-Id: FN-5151
Fusion-Task-Lineage: 17ebfc3f-6b6d-44a6-8243-7e8b8b140057

packages/dashboard/app/components/MessageComposer.tsx

@@ -48,10 +48,12 @@ export function MessageComposer({
   const [isSending, setIsSending] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const textareaRef = useRef<HTMLTextAreaElement | null>(null);
+  // Aligned with FN-5146 ChatView/QuickChatFAB 640px cap so pasted
+  // multi-paragraph messages stay visible without internal scroll.
   const { ref: autosizeRef } = useAutosizeTextarea({
     value: content,
     minHeight: 68,
-    maxHeight: 320,
+    maxHeight: 640,
   });
 
   const setTextareaRef = useCallback((node: HTMLTextAreaElement | null) => {