Convert from AppVeyor to GitHub Actions CI

[tillig]

Summary

• Replace AppVeyor CI with GitHub Actions reusable workflows
• Add MSBuild-based default.proj for build orchestration
• Add pre-commit hooks for linting (JSON, YAML, markdown, trailing whitespace)
• Update .editorconfig and .gitattributes to match standard Autofac template
• Rename Analyzers.ruleset to Source.ruleset, add Test.ruleset with SA1633/SA1214 suppression
• Replace conditional TestHost package references with FrameworkReference + explicit package
• Suppress ASPDEPR004/ASPDEPR008 deprecation warnings in tests
• Fix sample project ruleset references
• Add UTF-8 BOM to .cs files per editorconfig charset requirement
• Target .NET 10 SDK for builds

Test plan

• CI passes on this branch (build, test, dotnet-format, pre-commit)
• Disconnect AppVeyor after merge