feat(duo/claude): Added support for Claude Code

Description

This allows Duo Enterprise users to use claude code via the glab CLI. You can glab duo claude to access claude code once Claude code is installed on your machine to authenticate with GitLab

Related Issues

Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/563278

How has this been tested?

• Enable feature flag agent_platform_claude_code using chatops
• Install Claude code on your machine.
• Authenticate using glab auth login with gitlab.com
• Run glab duo claude to start Claude Code

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap