[CI] Add mutation testing for validation and security-critical helpers

[utksh1]

Problem

SecuScan needs a production-grade improvement in this area: Test quality for critical code..

Scope

Introduce mutation testing for validation, redaction, auth/security helpers, and document thresholds that avoid excessive runtime.

Acceptance Criteria

• The implementation is focused and does not introduce unrelated UI, docs, lockfile, or formatting churn.
• Security-sensitive behavior has explicit negative tests where applicable.
• Existing tests continue to pass, and new tests cover the main success and failure paths.
• Documentation or configuration examples are updated when operator behavior changes.

Verification

CI should run a targeted mutation job or scheduled workflow with a clear report artifact.

Difficulty

Hard, useful issue intended for experienced contributors.

[advikdivekar]

please assign me this under GSSoC 2026, sharing my implementation plan asap

[aaniya22]

Please assign this issue to me under Gssoc'26