ci: use npm ci and drop the unused jest toolchain

[Anexus5919]

📌 Related Issue

Fixes #897
Fixes #900
Fixes #901

---

📝 Description

Dependency, lockfile, and test-toolchain hygiene. These three are bundled because they all regenerate the root package-lock.json and depend on the same @testing-library/dom fix, so splitting them would mean three mutually-conflicting lockfiles.

🔹 What has been changed?

• CI uses npm install, not npm ci (and the root lockfile is out of sync, blocking npm ci) #897 (CI uses npm install, lockfile out of sync): CI installed with npm install, which ignores the lockfile (non-reproducible). Switching to npm ci requires package.json and the lockfile to be in sync, which they were not: @tensorflow/tfjs / @tensorflow/tfjs-layers are in package.json but were absent from the root lockfile, so npm ci failed on the frontend (the server/ lockfile was already in sync). Regenerated the root lockfile so it is in sync, and switched both CI install steps (frontend and backend) to npm ci.
• Orphan Jest toolchain (jest.config.cjs + jest devDeps) remains after vitest migration; CHANGELOG says removed #900 (orphan Jest toolchain): the project runs on vitest, but jest.config.cjs and the jest / ts-jest / jest-environment-jsdom / @types/jest devDependencies were left behind (the CHANGELOG already claims they were removed). Deleted the config file and the four orphan devDependencies. Kept @testing-library/jest-dom (the jest-dom matchers, used by the vitest setup).
• test:coverage fails: @vitest/coverage-v8 provider is not installed #901 (test:coverage provider missing): test:coverage runs vitest run --coverage, but no coverage provider was installed. Added @vitest/coverage-v8 pinned to vitest's version (4.1.7).
• Declared @testing-library/dom as a direct devDependency: regenerating with npm 10 otherwise drops it (it is only a transitive dep of @testing-library/react), which breaks React Testing Library under npm ci.

🔹 Why are these changes needed?

• npm ci gives reproducible, lockfile-pinned installs and is the correct command for CI, but it only works once package.json and the lockfile agree, which is the same out-of-sync state issue CI uses npm install, not npm ci (and the root lockfile is out of sync, blocking npm ci) #897 reports. The orphan Jest packages are dead weight after the vitest migration, and test:coverage is currently broken without the v8 provider. Pinning @testing-library/dom keeps the RTL setup working across lockfile regenerations.

---

🛠️ Type of Change

• 🐛 Bug Fix
• 🔧 Refactoring

---

🧪 Testing

✅ Tests Performed

• Tested locally
• npm ci --dry-run exits 0 for both the repo root and server/.
• Lockfile checks: @testing-library/dom@10.4.1 present; @tensorflow/tfjs@4.22.0 now present (was missing); vitest and @vitest/coverage-v8 both 4.1.7; jest / ts-jest / jest-environment-jsdom / @types/jest absent.
• Confirmed no source/config/script in the repo still references jest (test runner is vitest run).

🔹 Note on automated tests

Lockfile regenerated with npm install --package-lock-only (no node_modules write), so the local environment is untouched and the diff is limited to the lockfile metadata.

🌐 Browsers Tested

Not applicable (CI / dependency configuration).

---

📷 Screenshots / Demo (if applicable)

Not applicable.

---

📋 Checklist

• I have read the project's CONTRIBUTING guidelines
• My code follows the project style guidelines
• I have performed a self-review of my code
• I have tested my changes locally
• I have added/updated documentation where necessary (not applicable)
• My changes do not introduce new warnings or errors
• This PR is linked to an existing issue

---

💬 Additional Notes

Branched fresh from upstream/main and the lockfile regenerated against the current base, so it merges cleanly (the previous version of this branch conflicted only on the regenerated lockfile). Declaring @testing-library/dom directly also resolves the long-standing eviction, so React Testing Library component tests can run again under npm ci.

[vercel]

@Anexus5919 is attempting to deploy a commit to the somiljain2024-4175's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Anexus5919]

@Somil450 @diksha78dev Kindly have a review on this pr. Thanks!

[Anexus5919]

@Somil450 @diksha78dev Kindly have a review on this pr. Thanks!

[Anexus5919]

This failing check is from main, not this PR. Main's CI is currently broken (ShieldAlert used without importing it, plus untyped "privacy"/"terms&conditions" screens), so every PR goes red, even docs-only ones. Fix is up in #1039. Once it merges, a rebase turns this green. Merges cleanly with base.