docs: add macOS/Linux virtual environment activation command to backend setup

[Mohit-001-hash]

🔀 Pull Request

📌 Issue Reference

Closes #None

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📝 Summary

• What issue does this fix? This PR fixes a cross-platform compatibility issue where the local test suite would crash for contributors using Windows machines.
• What major changes were made? Updated the test script in package.json to use the cross-env package for setting environment variables (cross-env NODE_ENV=test). This ensures the test command works seamlessly across Windows, macOS, and Linux without throwing syntax errors.

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📸 Screenshots (if applicable)

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✅ Checklist

• My code follows the project's coding conventions
• I have tested all impacted features
• I have updated or added necessary documentation

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🔗 Related Issues / PRs

None

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🏅 Open Source Program Participation

Program Name: None

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💬 Additional Notes

None

[vercel]

@Mohit-001-hash is attempting to deploy a commit to the Durgeshwar's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Durgeshwar-AI]

@Mohit-001-hash Not clear.

[Mohit-001-hash]

Can you clarify what's not clear?

[Durgeshwar-AI]

Here you have updated only a single line. What I really wanted was a complete seperate sections showcasing how to run on windows seperatelty from the macOS/ Linux.