[Bug] ChartErrorMessage: error title "Data error" is not wrapped in t() — not translatable

Bug description

In ChartErrorMessage.tsx, the error title displayed when a chart fails to render is defined as a plain string constant:

const DEFAULT_CHART_ERROR = 'Data error';

This string is never passed through t(), so it cannot be translated. Users in non-English locales always see "Data error" regardless of their language setting.

Files

superset-frontend/src/components/Chart/ChartErrorMessage.tsx line 35

Fix

Import t from @apache-superset/core/translation and wrap the constant: const DEFAULT_CHART_ERROR = t('Data error');

### Screenshots/recordings

_No response_

### Superset version

master / latest-dev

### Python version

3.9

### Node version

16

### Browser

Chrome

### Additional context

_No response_

### Checklist

- [x] I have searched Superset docs and Slack and didn't find a solution to my problem.
- [x] I have searched the GitHub issue tracker and didn't find a similar bug report.
- [x] I have checked Superset's logs for errors and if I found a relevant Python stacktrace, I included it here as text in the "additional context" section.