feat: the vessel speaks in the séance — DeviceWhisper panel

Workstream D of the usability wave (#8). A compact live panel in the
séance side column, shown only when the seeker has paired hardware:
device name, online dot (reading within 60s), latest readings in the
terminal readout style, and cold-spot / pressure-anomaly flags from the
lib/coldSpot.ts cores. Fetches GET /api/device once on mount; renders
nothing on zero devices or fetch failure — the séance never sees an
error from this panel. Socket closed on unmount.

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

frontend/src/pages/SeancePage.tsx

@@ -24,6 +24,7 @@ import { GraphView } from '../components/GraphView'
 import { Transcript } from '../components/Transcript'
 import { EntityCard } from '../components/EntityCard'
 import { RitualPanel } from '../components/RitualPanel'
+import { DeviceWhisper } from '../components/DeviceWhisper'
 import { JudgmentPanel } from '../components/JudgmentPanel'
 import { TelemetryReadout } from '../components/TelemetryReadout'
 import { PlanchetteMachine } from '../lib/planchette'
@@ -362,6 +363,7 @@ function SeanceSession({ username }: { username: string }) {
             onToggleOpen={() => setDossierOpen((o) => !o)}
           />
 
+          <DeviceWhisper />
           <RitualPanel />
           <JudgmentPanel />