fix: require Node >=20 and use npm test --if-present in backend CI

[Anexus5919]

📌 Related Issue

Fixes #898
Fixes #899

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📝 Description

Two small build/CI metadata issues. The root engines.node claimed >=18.0.0, but vite@7 requires ^20.19 || >=22.12, vitest@4 requires ^20 || ^22 || >=24, and CI only tests 20.x/22.x, so Node 18 is neither supported nor tested. Separately, the backend CI step gated tests behind npm run | grep -q "test", a fragile parse of human-readable npm run output that also matches any script whose name merely contains "test".

🔹 What has been changed?

• BLD-5: bumped engines.node from >=18.0.0 to >=20.0.0 to match what the toolchain and CI actually require.
• BLD-6: replaced if npm run | grep -q "test"; then npm test; fi with npm test --if-present, the built-in npm mechanism for "run the script only if it exists."

🔹 Why are these changes needed?

• Declaring >=18 invites installs on a runtime the build tools reject. Bumping to >=20 makes the requirement honest. npm test --if-present is the standard, robust equivalent of the grep gate, with no dependence on the formatting of npm run output or accidental substring matches.

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🛠️ Type of Change

• 🐛 Bug Fix
• 🔧 Refactoring

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🧪 Testing

✅ Tests Performed

• Tested locally
• Confirmed engines.node is >=20.0.0 and package.json still parses as valid JSON.
• Confirmed the backend step uses npm test --if-present and no longer greps npm run output.

🔹 Note on automated tests

Metadata/CI-only changes; the dependency tree and lockfile are unaffected.

🌐 Browsers Tested

Not applicable (CI/package metadata).

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📷 Screenshots / Demo (if applicable)

Not applicable.

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📋 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

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💬 Additional Notes

Branched from upstream/main; merges cleanly with the current base (which still declares >=18 and the grep gate). This is the engines/backend-test pair; it does not change the install command (npm install vs npm ci), which is a separate item.

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[Anexus5919]

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

[Anexus5919]

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