Outages review fixes: reset on new target, memoize marker icons, coverage note in popup (#184)

- useOutagesIn kept the previous incident's answer while fetching the next
  one (IncidentPanel isn't keyed), so a newly selected incident briefly read
  'none reported here'. Drop the old answer when the target changes.
- OutageLayer built a fresh divIcon per marker every render; MapView
  re-renders on live updates, so Leaflet rebuilt every marker's DOM. Memoize.
- Popup now carries the provider's coverage note (ODIN: non-reporting
  utilities, e.g. Con Ed/O&R, show nothing even during an outage).

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

drb-frontend/components/map/OutageLayer.tsx

@@ -91,6 +91,7 @@ function OutagePopupBody({ a, feed }: { a: OutageArea; feed?: OutageProviderFeed
         </ul>
       )}
       <div className="text-[10px] text-ink-muted">County-level count — the marker is the county&apos;s centre, not where the outage is.</div>
+      {feed?.coverage_note && <div className="text-[10px] text-ink-muted">{feed.coverage_note}</div>}
       <SourceCredit credit={feed} fallbackName={feed?.name ?? a.provider}
         updated={[updated && `utility data ${updated}`, feed && `fetched ${fetchedLabel(feed.fetched_at) ?? "—"}`].filter(Boolean).join(" · ") || null} />
     </div>
@@ -163,7 +164,10 @@ export function OutageLayer({ shown }: { shown: boolean }) {
   const state = useMapOutages(map, shown);
   const areas = useMemo(() => state.data?.areas ?? [], [state.data]);
   const feeds = useMemo(() => new Map((state.data?.providers ?? []).map((p) => [p.id, p])), [state.data]);
-  const drawable = areas.filter((a) => a.lat != null && a.lon != null);
+  const drawable = useMemo(() => areas.filter((a) => a.lat != null && a.lon != null), [areas]);
+  // One icon per area per response: a fresh divIcon each render would make
+  // Leaflet rebuild every marker's DOM whenever MapView re-renders.
+  const icons = useMemo(() => new Map(drawable.map((a) => [a.id, outageIcon(a)])), [drawable]);
   const liveCount = areas.filter((a) => !a.stale && a.customers_out > 0).length;
   const staleCount = areas.filter((a) => a.stale).length;
   if (!shown) return null;
@@ -171,7 +175,7 @@ export function OutageLayer({ shown }: { shown: boolean }) {
     <>
       <OutageStatus map={map} state={state} liveCount={liveCount} staleCount={staleCount} />
       {drawable.map((a) => (
-        <Marker key={a.id} position={[a.lat!, a.lon!]} icon={outageIcon(a)} zIndexOffset={a.stale ? -100 : 100}
+        <Marker key={a.id} position={[a.lat!, a.lon!]} icon={icons.get(a.id)!} zIndexOffset={a.stale ? -100 : 100}
           title={`${countyName(a)}: ${a.stale ? "stale rows only" : `${a.customers_out.toLocaleString()} out`}`}>
           <Popup minWidth={240} maxWidth={320}>
             <OutagePopupBody a={a} feed={feeds.get(a.provider)} />