- Allow sshUser setting to override default 'git' user in insteadOf config
- When sshUser is empty, default to 'git@github.com'
- When sshUser is provided (e.g., 'customuser'), use 'customuser@github.com'
- Updated tests to verify custom SSH user behavior in auth configuration
Co-Authored-By: Claude:Qwen3-Coder-Next-4bit