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.

lib/pantallas/pantalla_buscar.dart

@@ -543,8 +543,17 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
     if (estado.cargando) {
       // S5-R6: shimmer placeholders instead of a bare spinner, consistent
       // with the loading pattern used by the home grid.
+      // Issue 3 (feedback-pruebas): row tier (12), not card tier (16) --
+      // these are background-less row placeholders, same tier as the real
+      // results below; the top inset is the standard section gap rather
+      // than the horizontal constant reused for a vertical axis.
       return Padding(
-        padding: const EdgeInsets.all(PluriLayout.horizontal),
+        padding: const EdgeInsets.fromLTRB(
+          PluriLayout.rowHorizontal,
+          PluriLayout.sectionGap,
+          PluriLayout.rowHorizontal,
+          PluriLayout.rowHorizontal,
+        ),
         child: Column(
           crossAxisAlignment: CrossAxisAlignment.start,
           children: [
@@ -579,8 +588,17 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
       // across the app -- favorites, the discovery grid -- which this
       // item does not touch).
       final query = _controller.text.trim();
+      // Issue 3 (feedback-pruebas): this card-tier state had NO top gap at
+      // all against the filter row above it -- the standard section gap
+      // now matches the other two mutually-exclusive results-area states
+      // (loading, populated) above.
       return Padding(
-        padding: const EdgeInsets.symmetric(horizontal: PluriLayout.horizontal),
+        padding: const EdgeInsets.fromLTRB(
+          PluriLayout.horizontal,
+          PluriLayout.sectionGap,
+          PluriLayout.horizontal,
+          0,
+        ),
         child: _TarjetaSinResultados(
           titulo:
               sinFiltros
@@ -616,7 +634,17 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
     return ListView.builder(
       shrinkWrap: true,
       physics: const NeverScrollableScrollPhysics(),
-      padding: const EdgeInsets.all(PluriLayout.horizontal),
+      // Issue 3 (feedback-pruebas): row tier (12), not card tier (16) --
+      // `FilaEmisoraPlana` rows are documented as "flat, background-less"
+      // (audit 6.5) but this padding never got updated to match when Tier 1
+      // introduced the 3-tier scale. The top inset is the standard section
+      // gap, not the horizontal constant reused for a vertical axis.
+      padding: const EdgeInsets.fromLTRB(
+        PluriLayout.rowHorizontal,
+        PluriLayout.sectionGap,
+        PluriLayout.rowHorizontal,
+        PluriLayout.rowHorizontal,
+      ),
       itemCount: total,
       itemBuilder: (context, i) {
         if (i >= resultados.length) {

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 {