extensions_ui: Improve error message when extensions fail to load (#43197)

<img width="500" height="1902" alt="Screenshot 2025-11-20 at 6  12@2x"
src="https://github.com/user-attachments/assets/daa5b020-17c8-4398-a64a-d691c566d6e7"
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Release Notes:

- extensions UI: Improved the feedback message for when extensions are
not being displayed due to a fetch error caused by lack of connection.
9667d7882aDanilo Leal committed on 11/20/2025, 9:28:11 PM· committed by GitHubparent6adb0f4
1 file changedLine totals unavailable