ci: integrate lightweight automated pip-audit dependency scanner

[Sahil07-codes]

Closes #308

Changes Implemented:

• Created a dedicated, lightweight .github/workflows/dependency-security.yml workflow running pip-audit.
• Configured the workflow to run isolated on Python 3.11 to maintain complete compatibility with the codebase's strict requirements layer.
• Appended local verification setup and execution steps to backend/README.md.

Verification Demo:
Tested the auditor locally within an active environment workspace. The scanner accurately caught and mapped existing dependency CVE records:

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[Sahil07-codes]

HI @imDarshanGK ,

i have submitted a PR regarding the Issue #352 , kindly review it and let me know about any furthur changes to be made.

[imDarshanGK]

@Sahil07-codes resolve conflicts

[Sahil07-codes]

Hi @imDarshanGK,

All automated checks and the security dependency auditing pipelines are now running successfully and passing green! The multi-way documentation merge conflicts have also been cleanly resolved.

The implementation is 100% stable, fully verified, and ready for your final review.

Thank you!