Add Vitest testing framework with React Testing Library

[devin-ai-integration]

Summary

This PR adds a unit testing framework to the CoreUI React Admin Template, which previously had no testing infrastructure. The setup includes Vitest as the test runner with React Testing Library for component testing.

Key additions:

• Vitest configuration with jsdom environment and JSX support for .js files
• Test setup with jest-dom matchers for DOM assertions
• 10 unit tests across 2 test files (AppFooter component and Redux store)

Review & Testing Checklist for Human

• Verify dependency installation: Dependencies were installed with --legacy-peer-deps due to React 19 compatibility. Run npm install --legacy-peer-deps and confirm no runtime errors occur when running npm test

• Check store test isolation: The Redux store tests in src/store.test.js dispatch actions that mutate global state. Tests may be order-dependent - verify tests pass when run individually and in different orders

• Validate JSX loader config: The vitest.config.mjs includes a workaround to treat .js files as JSX (lines 6-16). Confirm this doesn't cause issues with non-JSX .js files in the project

Recommended test plan:

1. Run npm install --legacy-peer-deps
2. Run npm test and verify all 10 tests pass
3. Run npm run test:coverage to check coverage reporting works
4. Optionally run npm run build to ensure the new dev dependencies don't affect production builds

Notes

Link to Devin run: https://partner-workshops.devinenterprise.com/sessions/b313c50a7c6e4ec8b18a4fb7f65c1508

[devin-ai-integration]

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