feat: Cold Spot Detector / Atmospheric Disturbance Index on Device Bay

Real-time anomaly visualization for temperature/pressure readings on the
device-feed dashboard, folklore's two most iconic paranormal markers:
sudden cold spots and rapid barometric swings.

- lib/coldSpot.ts: pure, directly-testable rolling-baseline tracker
  (time-aware EMA, since hardware doesn't report on a fixed schedule),
  cold-spot and pressure-anomaly classifiers, and a composite
  Atmospheric Disturbance Index that rewards correlated anomalies
  (a lone signal caps at 50/100; only both deviating together can
  reach 100) — modeled on evilMeter.ts's threaded-state pattern.
- components/ColdSpotPanel.tsx/.css: frost treatment + sparkline for
  temperature, ripple treatment for pressure, and a crescent-arc
  composite gauge (GhostLog's evil-meter gauge as the visual family
  reference) that only appears once a device has reported both sensors.
- DevicesPage.tsx: owns per-device baseline state, feeds it from
  `reading` frames, falls back to the existing generic row for any
  non-numeric temperature/pressure value.

26 new coldSpot.test.ts cases (warm-up, genuine vs. fluctuation,
correlated-vs-solo index, gappy/out-of-order data) and 7 new
DevicesPage integration tests. Full suite: 302/302 passing, tsc clean,
i18n coverage clean (en/es).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/i18n/en.json

@@ -474,6 +474,16 @@
         "open": "feed live",
         "unstable": "feed unstable…",
         "closed": "feed offline"
+      },
+      "coldSpot": {
+        "callout": "COLD SPOT — {{deviation}} {{unit}} below baseline"
+      },
+      "pressureAnomaly": {
+        "callout": "PRESSURE ANOMALY — {{magnitude}} {{unit}} swing, atmosphere shifting"
+      },
+      "disturbance": {
+        "title": "ATMOSPHERIC DISTURBANCE",
+        "ariaLabel": "atmospheric disturbance index"
       }
     }
   },