[Infra, PoC] Add static eval via skill-validator

[JanKrivanek]

Motivation

Add static non-LLM evaluation of skills by skill-validator from dotnet/skills
As a:

• nonblocking PR gate
• nightly run creating discussion item with report

Prereq

1. go to https://github.com/github/awesome-copilot/discussions/categories

2. Click New category

3. Set:

   • Name: Skill Quality Reports
   • Description: Automated nightly skills eval reports
   • Format: Announcement (so only the workflow bot can post, others can comment)
   • (+ optional - emoji)

4. Click Create

[Copilot]

Pull request overview

Adds GitHub Actions workflows to run the dotnet/skills skill-validator for static (non-LLM) evaluation of skills/agents, publishing a nightly quality report and posting PR feedback on changes.

Changes:

• Introduces a nightly scheduled workflow that scans all skills/ and agents/ and publishes results to a Discussions category (with Issue fallback).
• Adds a pull-request-triggered workflow that runs skill-validator on changed skills/agents and posts/updates a PR comment with findings.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
.github/workflows/skill-quality-report.yml	Nightly scan + report generation and publishing to Discussions/Issues.
.github/workflows/skill-check.yml	PR-time validation of changed skills/agents with a comment summarizing results.

Comments suppressed due to low confidence (1)

.github/workflows/skill-quality-report.yml:71

• Same issue as the skills scan: the agents scan pipes into tee, so $? reflects tee rather than skill-validator, causing exit_code to be unreliable. Capture the validator exit status via PIPESTATUS and/or enable pipefail.

          set +e
          AGENT_FILES=$(find agents -name '*.agent.md' -type f 2>/dev/null | tr '\n' ' ')
          if [ -n "$AGENT_FILES" ]; then
            .skill-validator/skill-validator check \
              --agents $AGENT_FILES \
              --verbose \
              2>&1 | tee sv-agents-output.txt
            echo "exit_code=$?" >> "$GITHUB_OUTPUT"
          else