test: add App component test coverage

[Hell1213]

Covers routing structure and component rendering behavior

Description

• Contributes: Add frontend test suites/cases for src #314

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

Tests BrowserRouter setup, route configuration, and component rendering for App.tsx

[github-actions]

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[Hell1213]

Added behavioral tests for App.tsx covering routing and component structure