Use per-command git config for GitHub App HTTPS credentials so private submodules authenticate without persisting global git config. Preserve configured git options for checkout, fetch, submodule, and LFS commands, and cover GitLab PR submodule checkout with tests.
- Add gitSshCommand parameter to setGitImportSettings and buildGitCheckoutCommand
- Extract hardcoded ssh commands to variables for consistency
- Apply custom ssh credentials to all git operations including submodule sync/update
- Configure git url rewriting for github token-based authentication with submodules
- Add comprehensive test suite for submodule credential propagation