CI/CD: Run Go vulnerability scanning

[jhelison]

Is your feature request related to a problem? Please describe.
Potential Go dependency vulnerabilities are only checked through Github security checks.

Describe the solution you'd like
Integrate a tool like gosec or go audit into CI to scan code and flag risky patterns.

Describe alternatives you've considered
Manual gosec runs locally.

Additional context
Add a CI job that fails on high-severity issues. Use cache if supported.