Add Copilot-Instructions label policy rule

[Demitrius Nelon (denelon)]

📖 Description

Adds a policy-bot rule to automatically apply a Copilot-Instructions label to pull requests that modify .github/copilot-instructions.md or any .github/instructions/*.instructions.md file, so reviewers get extra visibility when Copilot's guidance changes.

The rule triggers on PR Opened and Synchronize, matches files via regex, and is guarded with a
ot: hasLabel check so it won't re-fire once the label is already applied.

Created with GitHub Copilot's assistance.

🔗 References

Closes #303

🔍 Validation

• Validated the YAML with PowerShell's powershell-yaml module (ConvertFrom-Yaml).
• Cross-checked all conditions/actions against the documented GitOps.PullRequestIssueManagement policy schema.
• Confirmed no unrelated rules (e.g. the existing Needs-CLA first-time-contributor rule) were disturbed by this change.

✅ Checklist

• Signed the Contributor License Agreement
• Linked to an issue
• Updated documentation (if applicable)
• Updated Copilot instructions (if build, architecture, or conventions changed)

📋 Issue Type

• Bug fix
• Feature
• Task

Microsoft Reviewers: Open in CodeFlow

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