[tests] Add Jest runner and unit tests for src/utils (0% -> 97% coverage)

[devin-ai-integration]

Description

Coverage audit: the repo had no test runner — no jest/vitest dependency, no test script, and no config. The 46 existing src/**/index.test.js files are dead code: they import { shallow } from "enzyme" with enzyme-adapter-react-16 (see src/setupTests.js) while the site is on React 18, and none of those packages are installed. Effective coverage of the whole repo was 0%.

This PR adds a runner and covers the lowest-hanging, highest-value zero-coverage modules — the pure logic in src/utils:

module	coverage
slugify.js	100%
getCurrentPage.js	100%
getActiveServiceMesh.js	100%
currencies.js	100%
build-collections.js	100%
imageValidate.js	100%
redirects.js	100%
useHasMounted.js	100%
usedataList.js	100%
paginate.js	0% (see below)

src/utils overall: 0% -> 97.6% statements, 100% branches (39 tests, 9 suites, ~1s).

Setup details:

• jest.config.js uses jsdom and only picks up **/__tests__/**/*.test.js, so the legacy enzyme files are left untouched rather than failing the suite.
• The transform pins babel-preset-gatsby to targets: { node: "current" }; with the repo's browser targets the preset injects core-js/modules/* imports that aren't installed, and every suite fails to resolve.
• Hook tests (useHasMounted, usedataList) use createRoot + act from react directly, avoiding a new testing-library dependency.
• Added npm test / npm run test:coverage, and a "Run unit tests" step to .github/workflows/checks.yml.

Notes for Reviewers

Two incidental fixes needed to make npm test and committing tests work at all:

• Removed the stale pretest script (eslint --ignore-path .gitignore .): --ignore-path was removed in ESLint 9, so it aborted any npm test invocation.
• Added --no-warn-ignored to the ESLint command in .lintstagedrc.js. eslint.config.js ignores **/*.test.js and src/utils/, so with --max-warnings=0 the pre-commit hook failed on any staged test file (pre-existing for the legacy tests too).

Not covered, deliberately: src/utils/paginate.js is broken code, not just untested —

export const paginate = (pageNumber) => { setCurrentPage(pageNumber); };

setCurrentPage is not defined or imported, so calling it always throws ReferenceError. Nothing in the repo imports it. Happy to delete it in this PR if you'd prefer.

Signed commits

• Yes, I signed my commits.

Link to Devin session: https://app.devin.ai/sessions/6d93d15f5b444effa06fd52e61c6d516
Requested by: @NSTKrishna

[devin-ai-integration]

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