fix(aicli): handle detection for GitHub Copilot CLI version

[shubham-stepsecurity]

What does this PR do?

Type of change

• Bug fix
• Enhancement
• Documentation

Testing

• Tested on macOS (version: ___)
• Binary runs without errors: ./stepsecurity-dev-machine-guard --verbose
• JSON output is valid: ./stepsecurity-dev-machine-guard --json | python3 -m json.tool
• No secrets or credentials included
• Lint passes: make lint
• Tests pass: make test

Related Issues

[Copilot]

Pull request overview

This PR improves AI CLI tool detection by preventing false positives for the GitHub Copilot CLI when a VS Code extension shim is present on PATH and responds to --version with an installation prompt.

Changes:

• Add a VerifyFunc for github-copilot-cli that rejects the “not installed / install prompt” output and requires a version-like token.
• Add unit tests covering rejection of the install prompt and acceptance/parsing of a real Copilot CLI version.
• Adjust cleanVersionString to return "unknown" when no version token is found.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/detector/aicli.go	Adds Copilot-specific verification logic and tightens version parsing fallback behavior.
internal/detector/aicli_test.go	Adds tests for Copilot CLI detection behavior (shim prompt vs real version).

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