Is your feature request related to a problem?
When the backend returns an error (e.g., API is down, rate limit exceeded), the extension currently shows a standard browser alert() box, which is jarring and looks unprofessional.

Describe the solution you'd like
Instead of an alert, the error message should be displayed inside the injected UI container. The "Translating..." message could be replaced with a nicely styled error message (e.g., red text with an error icon).

Additional context
This involves modifying the handleElementClick function in content.js. In the catch block or when response.error is true, it should call the injectOrUpdateTranslations function with a special state that renders an error view instead of the tabbed code view.