[Nebula] Remove presence message when adding an error message (#5711)

Fixes: DASH-614

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---

## PR-Codex overview
This PR focuses on improving error handling in the `setMessages` function within the `ChatPageContent` component. It modifies how error messages are added to the message list, ensuring that the previous messages are preserved correctly.

### Detailed summary
- Refactored `setMessages` to create a new array `newMessages` based on previous messages.
- Added a condition to exclude the last message if its type is "presence".
- Pushed a new error message object containing the error details to `newMessages`.
- Returned `newMessages` from `setMessages`.

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Author: MananTank

apps/dashboard/src/app/nebula-app/(app)/components/ChatPageContent.tsx

@@ -242,13 +242,21 @@ export function ChatPageContent(props: {
         return;
       }
       console.error(error);
-      setMessages((prev) => [
-        ...prev,
-        {
+
+      setMessages((prev) => {
+        const newMessages = prev.slice(
+          0,
+          prev[prev.length - 1]?.type === "presence" ? -1 : undefined,
+        );
+
+        // add error message
+        newMessages.push({
           text: `Error: ${error instanceof Error ? error.message : "Failed to execute command"}`,
           type: "error",
-        },
-      ]);
+        });
+
+        return newMessages;
+      });
     } finally {
       setIsChatStreaming(false);
     }