chore: migrate gosec container image publishing and references to GHCR

[ccojocar]

Summary

• migrate GitHub Action runtime image to GHCR (ghcr.io/securego/gosec)
• pin action image tag to v2.24.6
• remove Docker Hub publishing from release workflow
• update docs, skills, and prompt text to reference GHCR
• add README notice that Docker Hub images will stop in the next release

Testing

• verified workflow/image references with repository searches

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.61%. Comparing base (88835e8) to head (ae3605e).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1567   +/-   ##
=======================================
  Coverage   80.61%   80.61%           
=======================================
  Files         104      104           
  Lines        9851     9851           
=======================================
  Hits         7941     7941           
  Misses       1421     1421           
  Partials      489      489           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.