settings: Show error notification when settings are invalid (#15905)

https://github.com/user-attachments/assets/07627142-e730-4446-a50b-7ef46f8e661c

We want to improve the design in the future, but it fixes a long
standing paper cut for now.

Release Notes:

- Added a popup that is displayed when the settings are invalid

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Co-authored-by: Thorsten <thorsten@zed.dev>