fix(favoritos): use the cross-version onReorder API and correct drag index math

The CI Flutter SDK predates v3.41 and only exposes ReorderableListView's
onReorder; the newer onReorderItem broke the build with three analyzer
errors. onReorder exists in both SDKs, so use it and compensate for its
pre-removal newIndex internally.

Fixing the call site surfaced a real ordering bug: _onReorder located the
target neighbour in the untrimmed global list, while ServicioFavoritos
.reordenar inserts into the list after the station is removed. Dragging a
station downwards past its neighbours therefore landed it one slot too far.
Adds a mid-list downward-drag test, the only case that separates the two
coordinate spaces.

lib/pantallas/pantalla_favoritos.dart

@@ -58,23 +58,35 @@ class _PantallaFavoritosState extends State<PantallaFavoritos> {
   /// global position [EstadoRadio.reordenarFavorito] expects, so a drag
   /// while a group chip is active still produces a coherent global order
   /// (other groups' relative order is left untouched).
+  ///
+  /// [newIndex] arrives in `ReorderableListView.onReorder`'s pre-removal
+  /// coordinate space: dragging downwards reports the slot the row would
+  /// occupy while it is still in the list. The logic below indexes into the
+  /// list AFTER the row is removed, so shift by one in that direction first.
   void _onReorder(
     List<Emisora> filtrados,
     List<Emisora> favoritos,
     int oldIndex,
     int newIndex,
   ) {
+    if (newIndex > oldIndex) newIndex -= 1;
     final movido = filtrados[oldIndex];
     final restantes = List<Emisora>.from(filtrados)..removeAt(oldIndex);
+    // `ServicioFavoritos.reordenar` removes the station first and THEN
+    // inserts at the index it is given, so the target index must be
+    // expressed in the global list WITHOUT the moved station. Locating the
+    // neighbour in the untrimmed list instead drifts by one whenever the
+    // moved station sits before it.
+    final globalSinMovido =
+        favoritos.where((e) => e.uuid != movido.uuid).toList();
     final int nuevoIndiceGlobal;
     if (restantes.isEmpty) {
-      nuevoIndiceGlobal = favoritos.length - 1;
+      nuevoIndiceGlobal = globalSinMovido.length;
     } else if (newIndex >= restantes.length) {
-      nuevoIndiceGlobal = favoritos.indexWhere(
-        (e) => e.uuid == restantes.last.uuid,
-      );
+      nuevoIndiceGlobal =
+          globalSinMovido.indexWhere((e) => e.uuid == restantes.last.uuid) + 1;
     } else {
-      nuevoIndiceGlobal = favoritos.indexWhere(
+      nuevoIndiceGlobal = globalSinMovido.indexWhere(
         (e) => e.uuid == restantes[newIndex].uuid,
       );
     }
@@ -217,7 +229,7 @@ class _PantallaFavoritosState extends State<PantallaFavoritos> {
           onTap: _abrirFormularioEmisoraPersonalizada,
         ),
       ),
-      onReorderItem:
+      onReorder:
           (oldIndex, newIndex) =>
               _onReorder(filtrados, favoritos, oldIndex, newIndex),
       children: [