fix(buscar): correct the gaps between the filter row and the results

Issue 3 (partial): the results area had no top gap against the filter
row in one state and reused the horizontal constant for a vertical axis
in another. Applies the 3-tier scale properly -- row tier for
background-less placeholders, card tier for card states.

The rest of the app's spacing review is still outstanding.

test/pantallas/pantalla_buscar_test.dart

@@ -15,6 +15,7 @@ import 'package:pluriwave/servicios/servicio_audio.dart';
 import 'package:pluriwave/tema/pluriwave_theme.dart';
 import 'package:pluriwave/tema/pluriwave_tokens.dart';
 import 'package:pluriwave/widgets/fila_emisora_plana.dart';
+import 'package:pluriwave/widgets/pluri_layout.dart';
 import 'package:pluriwave/widgets/tarjeta_emisora.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -835,6 +836,78 @@ void main() {
       );
     });
 
+    testWidgets('issue 3 (feedback-pruebas): the results list uses row-tier '
+        'horizontal padding (12), not the card-tier constant this "flat, '
+        'background-less row" was documented as needing but never got', (
+      tester,
+    ) async {
+      _setLargeSurfaceSize(tester);
+      final estado = _crearEstado(
+        radio: FakeServicioRadio(
+          busqueda: [emisoraDemo(uuid: 'r-1', nombre: 'Radio Uno')],
+        ),
+      );
+      addTearDown(estado.dispose);
+      await tester.runAsync(estado.inicializar);
+
+      await tester.pumpWidget(_conProviders(estado, _testApp()));
+      await _pumpStableFrame(tester);
+      await tester.enterText(find.byType(SearchBar), 'radio');
+      await tester.testTextInput.receiveAction(TextInputAction.done);
+      await _pumpStableFrame(tester);
+
+      final fila = find.byType(FilaEmisoraPlana);
+      expect(
+        tester.getTopLeft(fila).dx,
+        PluriLayout.rowHorizontal,
+        reason:
+            'issue 3: background-less rows are row tier (12), not card '
+            'tier (16)',
+      );
+    });
+
+    testWidgets('issue 3 (feedback-pruebas): the results list is topped by the '
+        'standard section gap, not the horizontal-inset constant reused for '
+        'a vertical axis', (tester) async {
+      _setLargeSurfaceSize(tester);
+      final estado = _crearEstado(
+        radio: FakeServicioRadio(
+          busqueda: [emisoraDemo(uuid: 'r-1', nombre: 'Radio Uno')],
+        ),
+      );
+      addTearDown(estado.dispose);
+      await tester.runAsync(estado.inicializar);
+
+      await tester.pumpWidget(_conProviders(estado, _testApp()));
+      await _pumpStableFrame(tester);
+      await tester.enterText(find.byType(SearchBar), 'radio');
+      await tester.testTextInput.receiveAction(TextInputAction.done);
+      await _pumpStableFrame(tester);
+
+      // Reads the structural padding directly, rather than measuring a
+      // gap between two rendered widgets — the count row's own height is
+      // dictated by its taller PopupMenuButton (48dp touch target), so a
+      // position-based gap measurement against the count TEXT specifically
+      // would be thrown off by that unrelated vertical centring.
+      //
+      // Scoped to `shrinkWrap: true` — the OUTER page ListView is ALSO an
+      // ancestor of every `FilaEmisoraPlana`, but only `_resultados`'s OWN
+      // inner `ListView.builder` sets `shrinkWrap`.
+      final listaResultados = tester.widget<ListView>(
+        find.byWidgetPredicate((w) => w is ListView && w.shrinkWrap),
+      );
+      final padding = listaResultados.padding as EdgeInsets;
+
+      expect(
+        padding.top,
+        PluriLayout.sectionGap,
+        reason:
+            'issue 3: the results list must use the dedicated vertical '
+            'section gap above its first row, not the horizontal (16) '
+            'constant reused for a vertical axis',
+      );
+    });
+
     testWidgets(
       'tapping the favourite toggle on a search result adds it to favorites',
       (tester) async {