Add _read_secret() helper that prefers *_FILE env vars (the standard Docker-secret pattern) over bare env vars. Strips trailing whitespace from file contents so printf/echo newlines don't break bcrypt verify. Existing CYCLONE_ADMIN_USERNAME + CYCLONE_ADMIN_PASSWORD still work for non-Docker deployments. Add tests/test_auth_bootstrap_file.py covering: file-path read, file-overrides-bare, bare-fallback, whitespace-stripping, missing-file raises.
Cyclone