chore: Add Agentic AI development assets for GitHub Copilot #151

Summary

Add Agentic AI development assets so that GitHub Copilot (agent mode) and other AI coding agents can build, test, and contribute to this repository correctly — following DSC Community conventions and DFSDsc-specific patterns.

Files to create

1. AGENTS.md (repository root)

• Repository overview — DFS (Distributed File System) DSC resources, supported Windows versions
• Resource type — MOF-based resources in source/DSCResources/
• Build commands:

  ./build.ps1 -Tasks noop   # one-time setup per pwsh session
  ./build.ps1 -Tasks build
  Invoke-Pester -Path 'tests/Unit' -Output Detailed

• Never run integration tests locally — CI only
• DSC Community resources — Guidelines, Blog Posts

2. tests/AGENTS.md

• Pester 5 syntax required; Pester 4 must not be used
• Should -Invoke, Should -BeTrue, BeforeDiscovery, $PSDefaultParameterValues
• Unit tests: tests/Unit/DSCResources/; Integration tests: tests/Integration/ (CI only)

3. .github/copilot-instructions.md

• DFSDsc identity, always update CHANGELOG.md, MOF-based resources, instruction file references
• Links: https://dsccommunity.org/guidelines/, https://dsccommunity.org/blog/

4. .github/instructions/*.instructions.md

Acceptance criteria

• AGENTS.md created at repository root
• tests/AGENTS.md created
• .github/copilot-instructions.md created
• All 10 .github/instructions/*.instructions.md files created with no SQL Server–specific content

References

• SqlServerDsc instruction files: https://github.com/dsccommunity/SqlServerDsc/tree/main/.github/instructions