chore: Refactor tests to use findBy queries for better async handling, update mock implementations, and clean up imports across various test files. Adjust toast utility to use for-of loops for callback execution. Update Vite and Vitest configuration files for consistency.

frontend/src/components/__tests__/LanguageSelector.test.tsx

@@ -1,7 +1,8 @@
-import { describe, it, expect, vi } from 'vitest'
 import { render, screen, fireEvent } from '@testing-library/react'
-import { LanguageSelector } from '../LanguageSelector'
+import { describe, it, expect, vi } from 'vitest'
+
 import { LanguageProvider } from '../../context/LanguageContext'
+import { LanguageSelector } from '../LanguageSelector'
 
 // Mock i18next
 vi.mock('react-i18next', () => ({