Add pink theme to code editor

[Copilot]

This PR adds a new "Pink" theme to the Pyret code editor with a very light pink background and complementary colors for all theme elements.

The pink theme features:

• Very light pink background (#fef8f8) that provides a gentle, barely perceptible pink tint
• Dark text (#2d1a1a) for excellent contrast and readability
• Harmonious color palette with purple keywords (#8e24aa), pink-tinted comments (#a85656), green strings (#2e7d32), and blue numbers (#1565c0)
• Comprehensive styling for all editor elements including syntax highlighting, check blocks, error states, tables, gutters, and UI components

Changes Made

1. Created src/web/css/themes/pink.css - Complete theme file with 124+ CSS variables following the same structure as existing themes
2. Updated src/web/editor.html - Added stylesheet link and "Pink" option to the theme selector dropdown

The theme integrates seamlessly with the existing theme system and provides users with a pleasant coding experience while maintaining full functionality and accessibility.

Fixes #601.

Warning

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• googlechromelabs.github.io

If you need me to access, download, or install something from one of these locations, you can either:

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[Copilot]

@shriram 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

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[shriram]

@copilot I don't want to add CoPilot instructions now. Please just add the theme.

[Copilot]

@copilot I don't want to add CoPilot instructions now. Please just add the theme.

Understood! The pink theme has been successfully implemented as requested in issue #601. The theme is complete with the very light pink background and all theme elements properly adjusted. No Copilot instructions will be added.