Fix onlineboard empty results and flights-map polyline zoom hazard

Online board: the /board endpoint treats dateFrom/dateTo as a half-open
interval, so sending the same date for both yielded zero rows on routes
that obviously have flights (e.g. SVO-LED). Mirror Angular's
OnlineBoardApiService.getFlightsByRoute and use dateTo = date + 1 day.

Flights map: two stacked problems made arcs disappear on zoom.
 - syncPolylines gated endpoints on map.hasLayer(marker); when
   syncVisibility removed a zoom-tier layer, its arc went with it.
 - The zoomend and toggle effects both called syncPolylines, which
   captured a stale closure from the first render (polylines = []) and
   wiped the layer. Polyline coords are geographic — Leaflet rescales
   them on zoom — so the rebuild was never necessary.
Arcs now render once per polylines prop change and stay put through
zoom and filter toggles.

src/features/flights-map/components/MapCanvas.test.tsx

@@ -452,7 +452,10 @@ describe("MapCanvas — polylines (C.3)", () => {
     expect(createdPolylines.length).toBe(0);
   });
 
-  it("skips intermediate cities whose marker is not on the map", () => {
+  it("draws multi-hop polylines through every city in the index", () => {
+    // Route/domestic filtering happens upstream in filterRoutes — by the time
+    // a polyline reaches MapCanvas, every city on its path is expected to be
+    // drawn, independent of zoom-tier visibility.
     render(
       <MapCanvas
         markers={[cm("A"), cm("B", "other"), cm("C")]}
@@ -461,11 +464,6 @@ describe("MapCanvas — polylines (C.3)", () => {
         tileUrl="t"
       />,
     );
-    const map = createdMaps[0]!;
-    // Reset so we count only polylines drawn by the next sync cycle.
-    createdPolylines.length = 0;
-    map.setZoom(6);
-    map.fireZoomend();
 
     expect(createdPolylines.length).toBe(1);
   });
@@ -487,7 +485,7 @@ describe("MapCanvas — polylines (C.3)", () => {
     expect(opts?.dashArray).toBe("4 14");
   });
 
-  it("rebuilds polylines on zoomend", () => {
+  it("does not rebuild polylines on zoomend (they are zoom-independent)", () => {
     render(
       <MapCanvas
         markers={[cm("A"), cm("B")]}
@@ -496,14 +494,17 @@ describe("MapCanvas — polylines (C.3)", () => {
       />,
     );
     const map = createdMaps[0]!;
-    map.setZoom(6);
-    map.fireZoomend();
-    const before = createdPolylines.length;
+    const afterInitialRender = createdPolylines.length;
 
     map.setZoom(4);
     map.fireZoomend();
+    map.setZoom(6);
+    map.fireZoomend();
 
-    expect(createdPolylines.length).toBeGreaterThan(before);
+    // Polyline coords are fixed by city lat/lng — Leaflet's SVG pane rescales
+    // them on zoom without us recomputing. Rebuilding from the zoomend
+    // handler also carried a stale-closure hazard.
+    expect(createdPolylines.length).toBe(afterInitialRender);
   });
 
   it("silently skips polylines with unknown city codes", () => {

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

@@ -324,10 +324,11 @@ export const MapCanvas: FC<MapCanvasProps> = ({
     }
     zoomLayersRef.current = zoomLayers;
 
-    // Rerun visibility + tooltip rules on every zoom change.
+    // Rerun visibility + tooltip rules on every zoom change. Polylines are
+    // zoom-independent (Leaflet rescales the SVG automatically) so no rebuild
+    // is needed here — rebuilding from a stale closure in fact wiped them.
     map.on("zoomend", () => {
       syncVisibility();
-      syncPolylines();
       syncTooltips();
     });
 
@@ -441,7 +442,6 @@ export const MapCanvas: FC<MapCanvasProps> = ({
   // --- Re-sync visibility + tooltips when toggles change ---
   useEffect(() => {
     syncVisibility();
-    syncPolylines();
     syncTooltips();
   }, [domestic, international]);
 

src/features/online-board/components/OnlineBoardSearchPage.tsx

@@ -61,6 +61,30 @@ function formatDateForApi(yyyymmdd: string): string {
   return yyyymmdd.includes("T") ? yyyymmdd : `${yyyymmdd}T00:00:00`;
 }
 
+/**
+ * Return the yyyyMMdd date one day after `yyyymmdd`. The API treats the
+ * board range as a half-open interval: `dateFrom=D, dateTo=D` yields zero
+ * rows. Matching Angular's OnlineBoardApiService.getFlightsByRoute.
+ */
+function addOneDayYyyymmdd(yyyymmdd: string): string {
+  const iso = yyyymmdd.includes("T") ? yyyymmdd.split("T")[0]! : yyyymmdd;
+  let year: number, month: number, day: number;
+  if (iso.includes("-")) {
+    const [y, m, d] = iso.split("-");
+    year = Number(y); month = Number(m) - 1; day = Number(d);
+  } else {
+    year = Number(iso.slice(0, 4));
+    month = Number(iso.slice(4, 6)) - 1;
+    day = Number(iso.slice(6, 8));
+  }
+  const dt = new Date(year, month, day);
+  dt.setDate(dt.getDate() + 1);
+  const y = dt.getFullYear().toString();
+  const m = (dt.getMonth() + 1).toString().padStart(2, "0");
+  const d = dt.getDate().toString().padStart(2, "0");
+  return `${y}${m}${d}`;
+}
+
 /**
  * Convert parsed online board URL params into API search params.
  * The API expects dateFrom/dateTo in yyyy-MM-ddT00:00:00 format.
@@ -69,9 +93,10 @@ function toSearchParams(
   params: OnlineBoardSearchPageProps["params"],
 ): SearchFlightsParams {
   const apiDate = formatDateForApi(params.date);
+  const apiDateTo = formatDateForApi(addOneDayYyyymmdd(params.date));
   const base: SearchFlightsParams = {
     dateFrom: apiDate,
-    dateTo: apiDate,
+    dateTo: apiDateTo,
   };
 
   switch (params.type) {