Add milestones capability

[alx-so]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, workflow, or canvas extension file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, workflow, or canvas extension with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the main branch for this pull request.

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Description

Add milestone management guidance to the github-issues skill.

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Type of Contribution

• New instruction file.
• New prompt file.
• New agent file.
• New plugin.
• New skill file.
• New agentic workflow.
• New canvas extension.
• Update to existing instruction, prompt, agent, plugin, skill, workflow, or canvas extension.
• Other (please specify):

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Additional Notes

@all-contributors add @alx-so for Skills

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[github-actions]

🔒 PR Risk Scan Results

Scanned 2 changed file(s).

Severity	Count
🔴 High	0
🟠 Medium	0
ℹ️ Info	0

✅ No matching risk patterns were detected in changed files.

This is an automated soft-gate report. Findings indicate review targets and do not block merge by themselves.

[github-actions]

🔍 Vally Lint Results

✅ All checks passed

Scope	Checked
Skills	1
Agents	0
Total	1

Severity	Count
❌ Errors	0
⚠️ Warnings	0
ℹ️ Advisories	0

Summary

Level	Finding
ℹ️	✅ github-issues (2/2 checks passed)
ℹ️	✓ [spec-compliance] All 1 skill(s) are spec-compliant.
ℹ️	✓ spec-compliance: All spec checks passed.
ℹ️	✓ [valid-refs] All file references across 1 skill(s) are valid.
ℹ️	✓ valid-refs: All file references resolve to existing files within the skill directory.
ℹ️	1 skill(s) linted, 1 passed

Full linter output

### Linting skills/github-issues
✅ github-issues (2/2 checks passed)
    ✓ [spec-compliance] All 1 skill(s) are spec-compliant.
        ✓ spec-compliance: All spec checks passed.
    ✓ [valid-refs] All file references across 1 skill(s) are valid.
        ✓ valid-refs: All file references resolve to existing files within the skill directory.

1 skill(s) linted, 1 passed

[Copilot]

Pull request overview

This PR extends the existing github-issues skill with milestone management guidance. It adds a new reference document describing how to create, read, update, close, reopen, delete, and manage issues within GitHub milestones via the REST API (gh api), and wires that reference into the skill's capability table and generated docs. This fits the repository's pattern of documenting extended capabilities in dedicated per-topic reference files that the agent loads on demand.

Changes:

• Added references/milestones.md documenting milestone CRUD operations and issue-to-milestone assignment using gh api.
• Registered the new capability in the SKILL.md "Extended Capabilities" table.
• Regenerated docs/README.skills.md so the github-issues row lists the new reference file.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
skills/github-issues/references/milestones.md	New reference file with gh api recipes for listing, getting, creating, updating, closing, reopening, deleting milestones and assigning/removing issues, plus usage rules.
skills/github-issues/SKILL.md	Adds a "Milestones" row to the Extended Capabilities table linking to the new reference.
docs/README.skills.md	Regenerated skills doc so the github-issues entry includes references/milestones.md.

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