docs: update README and user guide to reflect NuGet package caching functionality

[Copilot]

Pull Request

Description

Documentation described only the CLI infrastructure scaffolding, omitting the core feature: caching NuGet packages via [package]:[version] positional arguments. Updates README and user guide to accurately reflect what the tool does.

README.md

• Replace infrastructure-focused feature list with user-facing features (caching, path output, multi-package support)
• Add caching usage examples as primary examples in Usage section
• Add [package]:[version] to Command-Line Options table

docs/guide/guide.md

• Add NuGet package caching to Scope section
• Add Cache Packages section with single and multi-package examples + stdout path output note
• Add [package]:[version] to Command-Line Options table
• Add Example 4: Cache Multiple Packages

.cspell.json

• Add Newtonsoft as a known technical term (used in package examples)

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.NuGet.CacheTool --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

• 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

No code changes — documentation only.

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