feat: Add theme-aware WCAG colors with automatic Light/Dark switching

[willibrandon]

Description

The extension's colors failed WCAG AA compliance across both Light and Dark Visual Studio themes, using single hex colors that worked in one theme but were inaccessible in the other. This implementation adds automatic theme-aware color switching to ensure ≥4.5:1 contrast ratio in both themes without requiring user intervention.

Root cause: The SerilogClassificationFormats.cs used static colors like #007ACC that worked well in Light theme but failed accessibility standards in Dark theme. The README.md incorrectly claimed WCAG AA compliance when colors weren't actually accessible across both themes.

Solution:

• Implemented SerilogThemeColors service with VSColorTheme.ThemeChanged event handling for automatic theme detection
• Created SerilogClassificationFormatBase base class enabling automatic color updates when themes change
• Added WCAG AA compliant color palettes with semantic grouping (properties: blue family, operators: warm colors, functions: purple family)
• Converted all 15 classification format definitions to use modern C# 12 primary constructors with dependency injection
• Fixed ExpressionTemplate multi-line highlighting regression with deduplication logic to prevent overlapping classifications

Type of change

• Bug fix
• New feature
• Performance improvement
• Documentation update

Checklist

• Tests pass (.\scripts\test.ps1)
• Benchmarks checked (if performance-related)
• Documentation updated (if needed)

Additional notes

Fixes #9

[Copilot]

Pull Request Overview

This PR adds automatic theme-aware WCAG AA compliant colors for Serilog syntax highlighting. The extension now detects Visual Studio theme changes and automatically switches between Light and Dark color palettes without user intervention, ensuring ≥4.5:1 contrast ratio in both themes.

Key changes:

• Implemented automatic theme detection and color switching system
• Created WCAG AA compliant color palettes for both Light and Dark themes with semantic color grouping
• Modernized classification format definitions to use C# 12 primary constructors with dependency injection

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
SerilogSyntax.csproj	Added new classification classes and System.Drawing reference for color handling
ExpressionDetector.cs	Fixed ExpressionTemplate multi-line highlighting by removing specific string pattern requirement
SerilogThemeColors.cs	Core theme-aware color management service with VS theme detection and WCAG AA color palettes
SerilogTextProperties.cs	Data structure for text formatting properties (color, bold, italic)
SerilogClassifier.cs	Enhanced ExpressionTemplate detection with deduplication logic to prevent overlapping classifications
SerilogClassificationFormats.cs	Converted all format definitions to use theme-aware base class with dependency injection
SerilogClassificationFormatBase.cs	Base class enabling automatic color updates when themes change
ISerilogClassificationDefinition.cs	Interface for theme-aware classification definitions
README.md	Updated documentation to reflect theme-aware colors and WCAG compliance
ExampleService.cs	Cleaned up XML documentation comments

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