POST /api/model/set re-registered a named custom_providers row for any
custom/local main assignment, even when the endpoint was already a fact
in config.yaml (the CLI gateway setup writes provider: custom with an
inline base_url + api_mode). The picker then rewrote the CLI's shape into
custom:<slug> with base_url: '' (#76324).
Snapshot the pre-save config and skip registration when the endpoint is
already known (inline model.base_url, a providers: entry, or a
custom_providers row); only a genuinely new endpoint gets a named row.
Fixes#76324
da303d1729