The top-level ApplianceV1_6 model declared first_port_name /
port_name_format / port_segment_size but not custom_adapters, so the
GET /appliances endpoint (response_model=schemas.Appliance) stripped
custom_adapters from the response — the frontend never saw per-adapter
port names even though the appliance file and the server-side template
conversion (appliance_to_template reads it from the raw dict) handled it.
Add custom_adapters: Optional[List[CustomAdapterItem]] to ApplianceV1_6
so the field round-trips through the API. (ApplianceV8 already models it
inside its TemplateSetting.)