fix(chat): avoid Array.at in the mention range merge

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/home/components/user-message-content/utils.ts

@@ -48,7 +48,7 @@ export function computeMentionRanges(text: string, contexts: ChatMessageContext[
   ranges.sort((a, b) => a.start - b.start || b.end - a.end)
   const merged: MentionRange[] = []
   for (const range of ranges) {
-    if (range.start >= (merged.at(-1)?.end ?? 0)) merged.push(range)
+    if (range.start >= (merged[merged.length - 1]?.end ?? 0)) merged.push(range)
   }
   return merged
 }