Add k9scli.io feature

[Copilot]

Adds a devcontainer feature for k9s (Kubernetes TUI), based on the implementation outlined in #104.

New files

• src/k9scli.io/devcontainer-feature.json — feature metadata; exposes a version option (default: latest)
• src/k9scli.io/install.sh — downloads k9s from derailed/k9s GitHub releases; URL pattern: k9s_Linux_${arch}.tar.gz; arch mapping: amd64→amd64, arm64→arm64, armhf→arm, i386→386; installs to /usr/local/bin
• test/k9scli.io/test.sh — verifies k9s version output contains Version

CI

Added k9scli.io to both test-autogenerated and test-scenarios matrices in test.yaml.

Usage

"features": {
    "ghcr.io/devcontainer-community/devcontainer-features/k9scli.io:1": {}
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add k9scli.io feature</issue_title>
<issue_description>build on implementation in #104 </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add k9scli.io feature #117

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