Add Dependabot PR grouping configuration

[Copilot]

Pull Request

Description

Dependabot was creating individual PRs for each dependency update. Added grouping configuration to consolidate NuGet updates into single weekly PRs.

Changes:

• Added groups.nuget-dependencies with wildcard pattern to group all NuGet updates
• Set open-pull-requests-limit: 10 to cap concurrent PRs
• Set schedule.day: "monday" for predictable update timing

GitHub Actions remain ungrouped (intentional for individual security review).

Type of Change

• 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

Configuration validated against TemplateDotNetTool template patterns by repo-consistency-agent.

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