Live wall attention cues: NEW lane, pin pulse, opt-in tone and notifications (#238)

- lib/attention.ts: pure snapshot diff (Major opened, severity escalated,
  pursuit path gained a stop, priority keyword in a new transcript) with a
  silent baseline on page open; calls baseline separately on their first
  non-empty snapshot. Diffed over all active incidents so widening a filter
  is never "new"; emitted, laned and pulsed only for the FILTERED view.
- components/live/NewLane.tsx: "NEW · last 15 min" overlay above the rail
  (desktop) / compact chip (mobile), Gate A notice included.
- components/live/AttentionControls.tsx: opt-in Web Audio tone (enabling
  click unlocks audio) and Web Notifications while the tab is hidden, body
  carries the machine-output notice; prefs + keywords in localStorage.
- LiveView wires it and passes pulseIncidentIds to MapView (2 min pulse).
- useIncidents: useActiveIncidentsState exposes a loaded flag (first
  server snapshot) so the baseline never sees an empty pre-load list.
- MachineOutputNotice exports MACHINE_OUTPUT_NOTICE_TEXT (same wording).

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

drb-frontend/components/ui/MachineOutputNotice.tsx

@@ -50,6 +50,14 @@ function InfoGlyph({ className }: { className?: string }) {
 }
 
 const LEAD = "Machine-generated and unverified";
+const SHORT_BODY = "automated output, may contain errors.";
+
+/**
+ * The short notice as plain text, for surfaces that cannot render this
+ * component — e.g. a browser notification body (server-26#238). Same copy
+ * rules as above; it is the "popup"/"inline" wording verbatim.
+ */
+export const MACHINE_OUTPUT_NOTICE_TEXT = `${LEAD} — ${SHORT_BODY}`;
 
 interface Props {
   variant?: Variant;
@@ -62,7 +70,7 @@ export function MachineOutputNotice({ variant = "block", detail, className }: Pr
   const body =
     detail ??
     "transcripts, summaries and extracted details are automated output and may contain errors. Check the recording before acting on them.";
-  const shortBody = detail ?? "automated output, may contain errors.";
+  const shortBody = detail ?? SHORT_BODY;
 
   if (variant === "popup") {
     // Leaflet popups render on a white wrapper regardless of theme, so this