Add .github/copilot-instructions.md for Copilot cloud agent onboarding

[Copilot]

Adds a copilot-instructions.md to give Copilot cloud agents the context needed to work effectively in this repo without trial-and-error discovery.

Key contents

• Platform constraints — nanoFramework's critical API differences from standard .NET: no generics (all Type-based), no struct/array constructor params in DI, limited reflection, ArrayList/Hashtable instead of generic collections
• Build environment warning — .nfproj files require the nanoFramework MSBuild extensions on Windows; the agent's Linux environment cannot compile or run tests. Documents what is still actionable (source edits, docs, workflows, packages.config) vs. what must be validated by Azure Pipelines CI
• Testing — nanoFramework.TestFramework usage (not MSTest/xUnit), nanoCLR simulator setup via nano.runsettings, assertion API
• Package management — Old-style packages.config format, packages.lock.json enforcement in CI, and that lock files must be regenerated on Windows after version bumps
• Known issues — Struct DI limitation (tracked issue), GetImplementationType() gap with factory registrations, array constructor param null exception
• Repository map — Full directory layout, CI/CD topology (Azure Pipelines primary, GitHub Actions for PR checks), versioning via Nerdbank.GitVersioning

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud