feat(duo claude): improve error message when duo claude token retrieval is forbidden

Description

• feat(duo claude): improve error message when duo claude token retrieval is forbidden

Related Issues

Resolves #[issue_number]

How has this been tested?

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