Add self-validation test for --enforce flag

[Copilot]

Other projects rely on ReqStream's self-validation evidence to prove --enforce works, but no self-validation test existed for that code path — only unit tests.

Changes

Validation.cs — new RunEnforcementModeTest self-validation test (ReqStream_EnforcementMode):

• Verifies --enforce exits 0 when all requirements are covered by passing tests
• Verifies --enforce exits 1 when a requirement has no matching test result

requirements.yaml:

• VAL-002: adds ReqStream_EnforcementMode as test evidence
• PLT-001/002/004/005/006: adds platform/runtime-filtered variants (windows@, ubuntu@, dotnet8.x/9.x/10.x@) so platform requirements remain satisfied

ProgramTests.cs — Program_Run_WithValidateFlag_RunsValidation: updated expected counts from 4 → 5 and asserts the new test passes.

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 unit tests pass: dotnet test --configuration Release
• Self-validation tests pass:
  dotnet run --project src/DemaConsulting.ReqStream --configuration Release --framework net10.0
--no-build -- --validate
• 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 .

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

The self-validation test follows the same pattern as the existing RunTraceMatrixTest — creates a temp directory, writes fixture files, runs Program.Run(), and asserts on exit codes.

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