feat(hosts): the live strip shows the hottest sensor's temperature, get_host marks sensors that don't count, and the Monitors card's button reads "Add" (#6803)

- The host page's live strip gains a Temperature tile: temp_c_max (real
  thermometers only), its last 6 h and the sensor setting it, graded by
  Settings → Thresholds and counted in the header's worst reading, in °C.
- MCP get_host: each temperature carries `counted`; an unwired input is
  `counted: false` with `not_counted_because`, listed after the real ones.
  host_agent registers the judge (judge_sensors), so core imports no plugin.
- The Monitors card's "Add monitor" wrapped into two lines beside the
  uptime; it reads "Add", titled "Add a monitor for this host".

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

plugins/host_agent/__init__.py

@@ -29,6 +29,10 @@ def setup(app: "Quart") -> None:
     from steward.core.alerts import names_behind
     from .routes import name_hottest_sensor
     names_behind("host_agent", "temp_c_max", name_hottest_sensor)
+    # get_host over MCP marks the sensors the host's temperature leaves out.
+    from steward.mcp.tools.hosts import judge_sensors
+    from .routes import split_temps
+    judge_sensors(lambda host, temps: {k: why for k, (_c, why) in split_temps(host, temps)[1].items()})
     # A reboot the agent announced is silence with a reason, for a while (#5756).
     from datetime import datetime, timezone
     from steward.core.alerts import agents_away