The Actions runner only redacts values it knows about. Secrets written to
GITHUB_ENV via setup_dagger_remote.sh were never registered, so they could
appear in plain text in CI logs. Add ::add-mask:: calls for all exported
secrets (line-by-line for multiline values like SSH keys) and for the two
inline variables DAGGER_SSH_KEY and DAGGER_ENGINE_HOST.
Closes#434
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>