Make guard-sqlite-auth-split self-contained via _guard_file_exists so
orphan auth.db detection works when the script is sourced alone (unit
tests) while still preferring file_exists_as_betterdesk under entrypoints.
Align bootstrap credential tests with #385 (generate/export shared
password; publish ADMIN_PASSWORD to .admin_credentials).
Thanks: INSOLVE (Honorary); Marco Jakobs (@jacotec); MyNameisStitch (@MyNameisStitch); Redspin (@playerumpknow); muopc (@muopc)
Fresh Docker installs without ADMIN_PASSWORD generated two different random
passwords: Go wrote /opt/rustdesk/.admin_credentials while the panel
authenticated against auth.db seeded by Node.js. Pre-bootstrap a shared
password in entrypoints before supervisord / server start.
Refs #385
Thanks: INSOLVE (Honorary); Marco Jakobs (@jacotec); MyNameisStitch (@MyNameisStitch); Redspin (@playerumpknow)