add GitHub dev

[baxyz]

• implement github-dev feature with CLI and extensions
• add auto-authentication script for gh CLI
• update essential-dev description for clarity
• create tests for github-dev feature

Description

Please include a summary of what this PR does and why it's needed.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring
• Test improvement

Related Issues

Closes #(issue number)

How Has This Been Tested?

Describe the tests you ran and how to reproduce them:

• Test A
• Test B

Checklist

• My code follows the code style of this project
• I have updated the documentation accordingly
• I have added tests for my changes
• All new and existing tests passed locally
• My commits follow the conventional commit format

Screenshots (if applicable)

Add screenshots for UI changes.

Additional Context

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[github-actions]

✅ PR Validation Passed

All checks passed!

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📋 Pipeline Status

	Job	Status
✅	🧾 Conventional Commits	passing
✅	🧪 Feature Tests	passing
✅	🐚 ShellCheck	passing

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_{🤖 Generated by @helpers4 CI • 2026-04-18}

[Copilot]

Pull request overview

Adds a new github-dev DevContainer Feature to centralize GitHub tooling (GitHub CLI + VS Code GitHub extensions) and updates repository docs/CI to reflect the new feature and the slimmer essential-dev.

Changes:

• Introduce src/github-dev feature (gh install + auto-auth profile.d script + VS Code extension bundle) with a new feature test.
• Reposition essential-dev to exclude GitHub-specific tooling and update docs/index + conventional-commit scopes accordingly.
• Extend CI matrices to test github-dev on Debian and the DevContainers Ubuntu base image.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/github-dev/install.sh	New installer for gh + installs /etc/profile.d/gh-auth.sh.
src/github-dev/gh-auth.sh	Auto-auth script that logs gh in when a token is present.
src/github-dev/devcontainer-feature.json	Feature metadata + ghVersion option + VS Code extensions/settings.
src/github-dev/README.md	Usage/options/docs for the new feature.
test/github-dev/test.sh	New feature test validating gh + auth script presence.
src/essential-dev/devcontainer-feature.json	Updates essential-dev version/description + removes GitHub tooling extensions.
README.md	Adds github-dev section and updates feature list/descriptions.
AGENTS.md	Adds github-dev scope and updates the feature table.
.github/workflows/test.yml	Adds github-dev to CI feature test matrix.
.github/workflows/pr-validation.yml	Adds github-dev to PR validation scopes + feature test matrix.

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