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>

steward/static/steward.css

@@ -446,7 +446,9 @@ a.stat-tile:hover { border-color: var(--border-mid); background: var(--bg-elevat
 .host-health-summary { font-size: 0.92rem; }
 /* Its four tiles share the card's width (two a row on a phone); each sparkline
    stretches across its tile. */
-.host-health-tiles { grid-template-columns: repeat(4, minmax(0, 1fr)); }
+.host-health-tiles { grid-template-columns: repeat(var(--tiles, 4), minmax(0, 1fr)); }
+/* Which sensor the temperature tile reads, under its line; cut with … when long. */
+.stat-tile-sensor { display: block; font-size: 0.72rem; color: var(--text-muted); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
 .host-health-tiles .stat-tile { min-width: 0; }
 .host-health-tiles .stat-tile-hint { margin-top: 0.25rem; }
 @media (max-width: 640px) { .host-health-tiles { grid-template-columns: repeat(2, minmax(0, 1fr)); } }