The frontend takes the first host of a comma-separated override
(`splitFirstHost`), the backend took the whole string — so a two-host
override checked a hostname the UI never links to. `_parse_override`
now splits the same way.
The WebSocket service-status entry also declares `host` (nullable, as
the backend sends it), so the overlay key stops relying on an
undeclared field.
ha-relevant: yes