Fix cryptography vulnerability CVE-2026-69247 (#225)

[ritiksah141]

Summary

Upgrades the direct cryptography dependency from 49.0.0 to 50.0.0 to remediate CVE-2026-69247 reported by Dependabot alert #13.

What changed

• Updated the cryptography pin to the first patched release.
• Added the remediation to the Unreleased security changelog.

Verification

• pip-audit reports no known vulnerabilities.
• Backend suite: 480 passed, 2 skipped, 84.21% coverage.
• Ruff, Bandit, frontend lint/build, and website tests pass.

Closes #225

[Vishnu2707]

Thanks for fixing this on priority, merging this asap!

cryptography version 44.0.0 through 49.x has a known vulnerability (CVE-2026-69247, PKCS#7), fixed upstream in 50.0.0. The upgrade here looks the right choice, hence rolling out on priority basis as it is in prod.