Fix dragend: update waypoint through proxy, not stale closure reference

src/Planner.svelte

@@ -75,9 +75,11 @@
     const wp = { lng, lat, marker };
     marker.on('dragend', () => {
       const { lng: newLng, lat: newLat } = marker.getLngLat();
-      wp.lng = newLng;
-      wp.lat = newLat;
-      waypoints = waypoints; // trigger reactivity
+      const i = waypoints.findIndex(w => w.marker === marker);
+      if (i >= 0) {
+        waypoints[i].lng = newLng;
+        waypoints[i].lat = newLat;
+      }
       fetchRoute();
     });