Custom providers that have a curated models: list in config.yaml
(e.g. ZenMux gateways) should show ONLY those configured models in
the picker dropdown, not the full /v1/models catalog.
Before this fix, _named_custom_groups unconditionally called
_read_custom_endpoint_models() which would pull hundreds of models
from aggregator gateways and overwrite the user's curated list.
Now the build checks if the custom_provider entry has a non-empty
models dict/list in config.yaml — if so, it skips the live fetch
and uses only the configured models (same behavior as hermes-agent
model_switch.py Section 4 patch).
Closes: configure-model-list-should-be-authoritative
Colin Chang
9c3e37d2ee