fix: backend prod dockerfile

[Nabhag8848]

Description

• [x] includes environment variables as ARG in dockerfile so railways env will be used in container. https://docs.railway.app/guides/dockerfiles#using-variables-at-build-time

Fixes # (issue)

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[vercel[bot]]

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[github-actions[bot]]

Thank you for following the naming conventions for pull request titles! 🙏