Host signals: the Orin's health on yukart/host/<signal> (source host)

Temperatures, CPU/GPU load, memory, module power, fan, WiFi/LTE/tablet
links and the UPS battery, published by svc-core's orin-status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

schema/envelope.json

@@ -2,7 +2,7 @@
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "$id": "https://yukart/schema/envelope.json",
   "title": "Signal envelope",
-  "description": "Every decoded signal published on yukart/vehicle/* and yukart/gnss/*. Raw CAN uses the binary frame encoding instead.",
+  "description": "Every decoded signal published on yukart/vehicle/*, yukart/gnss/* and yukart/host/*. Raw CAN uses the binary frame encoding instead.",
   "type": "object",
   "required": [
     "timestamp",