Add comprehensive GitHub Copilot instructions with validated CDN access and environment configuration for CSS DSL repository

[Copilot]

This PR adds comprehensive GitHub Copilot support to the CSS DSL repository with both detailed instructions and a standardized environment configuration that mirrors the CI workflow.

Key Features

Comprehensive Copilot Instructions (.github/copilot-instructions.md)

• Detailed build & test instructions with exact SBT 1.11.3 installation commands
• Complete project navigation guide for 14 generated subprojects (Bootstrap 3/4/5, Bulma, Semantic UI, Fomantic UI, Font Awesome)
• Cross-compilation instructions for Scala 2.13.16 and 3.3.6
• Timing expectations and timeout recommendations (90+ seconds for tests)
• Framework support matrix with current versions and target library mappings
• Troubleshooting guide for common issues

Validated Network Access

• Documents confirmed CDN access to cdn.jsdelivr.net and stackpath.bootstrapcdn.com
• Explains the code generation process: CSS download → parsing → Scala DSL generation
• Provides clear build validation examples with working network connectivity

Environment Configuration (.github/copilot/environment.yml)

• Mirrors the existing CI workflow setup exactly (ubuntu-latest, Java 11 temurin, SBT 1.11.3)
• Includes validated CDN access verification commands
• Documents supported Scala/Java versions matching CI matrix
• Provides validation commands for SBT installation, project loading, and compilation
• Explains project-specific requirements (no src/ directories, network dependencies)

Project Structure Documentation

• Explains dynamic project generation (subprojects created at build time)
• Documents the unique architecture where code is generated from downloaded CSS files
• Provides commands for project switching and dependency inspection

The environment configuration ensures GitHub Copilot agents work in conditions identical to the CI environment, improving reliability and consistency for code generation tasks.

Fixes #374.

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[nafg]

@copilot I added the urls to the allowlist

[nafg]

@copilot what about https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment, base it on the existing ci workflow

[Copilot]

@copilot I added the urls to the allowlist

Thanks! Confirmed that CDN access is now working. I successfully tested builds with both cdn.jsdelivr.net and stackpath.bootstrapcdn.com. Updated the documentation to reflect the allowlisted access and removed the network limitation warnings. Commit d4fbc8e.

[Copilot]

@copilot what about https://docs.github.com/en/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment, base it on the existing ci workflow

Created .github/copilot/environment.yml based on the existing CI workflow. The environment configuration mirrors the CI setup exactly:

• Ubuntu latest OS with Java 11 (temurin) and SBT 1.11.3
• CDN access verification for cdn.jsdelivr.net and stackpath.bootstrapcdn.com
• Validation commands for SBT installation, project loading, and compilation
• Support for Scala 2.13.x and 3.3.x cross-compilation
• Project-specific documentation (no src/ directories, 14 generated projects)

Also updated copilot-instructions.md to reference the new environment configuration. This ensures GitHub Copilot agents work in conditions identical to the CI environment. Commit 7aa849d.

[Copilot]

Pull Request Overview

This PR adds comprehensive GitHub Copilot instructions and environment configuration to the CSS DSL repository to improve agent functionality and developer experience. The changes enable Copilot to work effectively with this specialized code generation project that requires external CDN access.

• Establishes GitHub Copilot agent environment configuration that mirrors the CI workflow setup
• Documents comprehensive build, test, and navigation instructions for the CSS DSL generator
• Configures allowlisted CDN access validation for CSS framework downloads

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 3 comments.

File	Description
.github/copilot/environment.yml	Defines Copilot agent environment with CI-matching setup, CDN validation, and project-specific configuration
.github/copilot-instructions.md	Provides detailed instructions for working with the CSS DSL generator, including network requirements and project structure

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