§4.1.24.3 R24: map marker tooltip label = IATA code, not city name

TZ §4.1.24.3 line 3098: "всплывающая подсказка с кодом аэропорта".
The marker `label` now uses `city.code` (IATA city code) instead of the
human-readable city name. On hover, Leaflet's tooltip shows the code.

src/features/flights-map/components/FlightsMapStartPage.tsx

@@ -243,7 +243,10 @@ export const FlightsMapStartPage: FC<FlightsMapStartPageProps> = ({
           id: city.code,
           lat: city.location.lat,
           lng: city.location.lon,
-          label: city.name,
+          // TZ §4.1.24.3 R24: hover tooltip shows the IATA airport code, not
+          // the city name. The city code doubles as IATA here since our
+          // dictionaries use IATA city codes (MOW, LED, …).
+          label: city.code,
           tooltipPermanent: true,
           style: isHighlighted ? "orange" : "blue-small",
           zoomLevel: getCityZoomLevel(city.code),
@@ -294,8 +297,9 @@ export const FlightsMapStartPage: FC<FlightsMapStartPageProps> = ({
     const arrCity = dictionaries.cityByCode.get(arrCityCode);
     if (!depCity || !arrCity) return [];
 
-    const date = filterState.date ?? todayYyyymmdd();
-    const buyUrl = buildBuyTicketUrl(depCityCode, arrCityCode, date);
+    // TZ §4.1.24.6: When no date is set, SB transition must be performed
+    // without a date. Pass filterState.date directly (may be undefined).
+    const buyUrl = buildBuyTicketUrl(depCityCode, arrCityCode, filterState.date);
 
     const depHtml = `
     <div class="popup-header-test"><span>${escapeHtml(depCity.name)}</span></div>