Align BuildMark with TemplateDotNetTool template updates

[Copilot]

Pull Request

Description

Syncs BuildMark with recent TemplateDotNetTool template changes across agent docs and project configuration.

Agent Documentation (.github/agents/)

• test-developer.md: Added Test Source Filters + MSTest V4 Best Practices sections; new Assert.StartsWith antipattern (template PR Use BuildMark-generated build notes in GitHub releases #45)
• code-quality-agent.md: Fix markdownlint config reference → .markdownlint-cli2.jsonc
• requirements-agent.md: Added Test Source Filters section
• technical-writer.md: Clarified reference-style vs inline link rules; explicit exception for agent markdown files
• software-developer.md: Fixed XML Docs rule — four-space indentation sub-rule

Project Files

• src csproj: LangVersion 12 → latest, GenerateDocumentationFile True → true, add section comments, SonarAnalyzer.CSharp → 10.20.0.135146, add Polyfill 9.12.0 (template PR Comprehensive documentation update using SarifMark template #41)
• test csproj: Same LangVersion/GenerateDocumentationFile fixes, add section comments, add <Using Include="Polyfills" /> (template PR [Feature]: Requirements and Trace Matrix #46), Microsoft.NET.Test.Sdk → 18.3.0, SonarAnalyzer.CSharp → 10.20.0.135146

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code quality improvement

Related Issues

Pre-Submission Checklist

Before submitting this pull request, ensure you have completed the following:

Build and Test

• Code builds successfully: dotnet build --configuration Release
• All tests pass: dotnet test --configuration Release
• Code produces zero warnings

Code Quality

• Code formatting is correct: dotnet format --verify-no-changes
• New code has appropriate XML documentation comments
• Static analyzer warnings have been addressed

Quality Checks

Please run the following checks before submitting:

• Spell checker passes: cspell "**/*.{md,cs}"
• Markdown linter passes: markdownlint "**/*.md"
• YAML linter passes: yamllint '**/*.{yml,yaml}'

Testing

• Added unit tests for new functionality
• Updated existing tests if behavior changed
• All tests follow the AAA (Arrange, Act, Assert) pattern
• Test coverage is maintained or improved

Documentation

• Updated README.md (if applicable)
• Updated ARCHITECTURE.md (if applicable)
• Added code examples for new features (if applicable)
• Updated requirements.yaml (if applicable)

Additional Notes

Template PRs addressed: #41 (Polyfill package + LangVersion: latest), #45 (Assert.StartsWith antipattern), #46 (Polyfills implicit using), #44 (boolean capitalization fix).

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