ci: remove mend workflow and references

[javorszky]

Proposed changes

Same as #10574, but cherry picked manually against release-2026-lts

Remove Mend (formerly WhiteSource) software composition analysis scan workflow, release pipeline jobs, bot allowlist entries, labeler patterns, and associated documentation.

• Delete .github/workflows/mend.yml
• Remove mend job from .github/workflows/release.yml and .github/workflows/release-lts.yml
• Remove mend from allowlist in .github/workflows/f5-cla.yml
• Remove '^mend/' branch pattern from .github/labeler.yml
• Remove .github/workflows/mend.yml from .github/scripts/exclude_ci_files.txt
• Update CI pipeline documentation in .github/skills/nic-ci-pipelines/SKILL.md

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.20%. Comparing base (dc867f6) to head (0fae5f1).

Additional details and impacted files

@@                Coverage Diff                @@
##           release-2026-lts   #10606   +/-   ##
=================================================
  Coverage             55.20%   55.20%           
=================================================
  Files                    97       97           
  Lines                 19651    19651           
=================================================
  Hits                  10848    10848           
  Misses                 8193     8193           
  Partials                610      610           

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[github-actions]

Package Report

Details

gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus, 37.0.4-1~trixie, amd64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-njs, 37.0+1.0.0-1~trixie, amd64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-otel, 37.0+0.1.2-1~trixie, amd64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-fips-check, 37.0+0.1-1~trixie, amd64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-agent, 3.11.3~trixie, amd64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus, 37.0.4-1~trixie, arm64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-njs, 37.0+1.0.0-1~trixie, arm64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-otel, 37.0+0.1.2-1~trixie, arm64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-plus-module-fips-check, 37.0+0.1-1~trixie, arm64
gcr.io/f5-gcs-7899-ptg-ingrss-ctlr/dev/nginx-ic/nginx-plus-ingress:t-e824c3c5d869de3cc1993ec4a01a80d3, nginx-agent, 3.11.3~trixie, arm64