SystemConfigDto validation error on Grocy 4.7.0: USER_USERNAME missing from /api/system/config

[Araquis]

Describe the bug
Setting up the integration against a fresh Grocy 4.7.0 instance fails during
async_setup_entry with a pydantic ValidationError. Connectivity and the API
key both work fine (confirmed the key manually against /api/system/info
and /api/chores) — the failure is specific to /api/system/config.

Traceback

File "/config/custom_components/grocy/grocy_data.py", line 103, in wrapper
    config = self.api.system.config()
  File ".../grocy/managers/system.py", line 37, in config
    raw = self._api.get_system_config()
  File ".../grocy/grocy_api_client.py", line 1142, in get_system_config
    return SystemConfigDto(**parsed_json)
pydantic_core._pydantic_core.ValidationError: 1 validation error for SystemConfigDto
USER_USERNAME
  Field required [type=missing, input_value={'MODE': 'production', ...}, input_type=dict]

Root cause
grocy-py==1.0.0's SystemConfigDto (grocy_api_client.py) requires
USER_USERNAME on /api/system/config. Grocy 4.7.0 (released 2026-08-28)
no longer returns USER_USERNAME when the request is authenticated with an
API key only (no browser session) — there's no "logged in" user to report.

Environment

• Grocy: 4.7.0 (linuxserver/grocy docker image)
• custom-components/grocy: 1.16.0 (installed via HACS)
• grocy-py: 1.0.0 (latest on PyPI)
• Home Assistant Core: 2026.8.3 (docker, ghcr.io/home-assistant/home-assistant:stable)

Expected behavior
username in SystemConfigDto should be Optional[str] = None, or the
client should tolerate a missing USER_USERNAME key generally when
authenticating via API key rather than session.

Workaround
None found — the config entry fails to set up at all since
_async_get_available_entities requires async_get_config() to succeed.