Add transient empty payload protection for hosts data, matching the
existing protection for dockerHosts. When a websocket message contains
an empty hosts array (transient state), the UI now waits for 3
consecutive empty payloads before applying the change.
This prevents the "Host" type badge from disappearing intermittently
in Settings → Agents → Managed Agents when the unified agent is
reporting both host and docker data.
Related to #773
6c1a0815ea