Follow-up cleanup on the OpenViking setup path merged in #48262:
- _write_ovcli_config now uses utils.atomic_json_write(path, data, mode=0o600)
instead of the local _precreate_secret_file + write_text + chmod sequence.
The shared helper (already used by honcho/mem0/supermemory/hindsight) writes
via temp-file + fchmod(0600) + fsync + os.replace, so the ovcli.conf is
written atomically (no half-written secret file on crash) and with no
chmod-after-write TOCTOU window. _precreate_secret_file stays for the .env
writer path.
- Remove dead _DEFAULT_ACCOUNT/_DEFAULT_USER constants (0 references; the
empty->'default' tenant fallback lives in the _VikingClient constructor).
Tests: tests/plugins/memory/test_openviking_provider.py + test_memory_setup.py
+ openviking_plugin/test_openviking.py -> 130 passed; ruff clean.