_spawn_gateway_restart() now calls _reap_unsupervised_gateway_orphans()
before spawning a new `hermes gateway restart` child. On desktop-app
restart the old serve exits but its gateway child gets reparented to
launchd (PPID=1) and keeps its platform connection alive. The new
serve then spawns a fresh gateway, resulting in two live gateways
racing the same connection.
The reap was already implemented for the CLI restart path (#75936) but
the dashboard's _spawn_gateway_restart path was not covered.
Fixes#77276
RelaxJonh