MIDI alarm when the Lighting PC drops out of NA Tracks' session (FX lights)

Tracks sends the FX lighting cues to the Lighting PC through NA Tracks'
network MIDI session. A midi_peer check may now name a "host": the watchdog
reads that Mac's sessions over SSH every 5 s, sending this folder's
coremidi.py over stdin (nothing installed there). Unreachable = no verdict;
the Tracks Mac's own ping check covers that.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config.json

@@ -98,6 +98,7 @@
     { "id": "midi", "label": "MIDI", "pos": [2, 3], "checks": [
       { "type": "midi_peer", "session": "NA Ingest", "peer": "Lighting PC", "tag": "LIGHT PC" },
       { "type": "midi_peer", "session": "NA Ingest", "peer": "SuperRack-LiveBox", "tag": "SUPERRACK" },
+      { "type": "midi_peer", "host": "tracks", "session": "NA Tracks", "peer": "Lighting PC", "tag": "FX LIGHTS" },
       { "type": "mdns", "instance": "Lighting PC", "name": "LIGHT PC MIDI" },
       { "type": "mdns", "instance": "NA Tracks", "name": "TRACKS MIDI" },
       { "type": "midi_rx", "source": "Network NA Ingest Listen", "name": "TRACKS IN" }