fix(favoritos): stop the header padding from doubling up

Issue 3 (feedback-pruebas): ReorderableListView.padding wrapped
header/rows/footer with a single horizontal value (16), which doubled
up on top of PluriRootHeader's own internal inset -- landing the
title at 36px instead of the 20px every other root uses -- while also
applying card-tier padding to the flat FilaEmisoraPlana rows (row
tier, matching the same widget's fix on Buscar) and leaving the
populated-state top gap at an unwired 4 that didn't match this same
screen's own empty state (0) or the footer CTA's prototype value (8).

Zeroes the list-level padding and gives the header, chip strip, rows,
and footer CTA their own correctly-tiered insets instead.

test/pantallas/pantalla_favoritos_test.dart

@@ -7,7 +7,9 @@ import 'package:pluriwave/l10n/gen/app_localizations.dart';
 import 'package:pluriwave/pantallas/ajustes/pantalla_ajustes_grupos_favoritos.dart';
 import 'package:pluriwave/pantallas/pantalla_favoritos.dart';
 import 'package:pluriwave/widgets/fila_emisora_plana.dart';
+import 'package:pluriwave/widgets/pluri_layout.dart';
 import 'package:pluriwave/widgets/pluri_push_scaffold.dart';
+import 'package:pluriwave/widgets/pluri_root_header.dart';
 import 'package:pluriwave/widgets/tarjeta_emisora.dart';
 import 'package:provider/provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -546,6 +548,106 @@ void main() {
       expect(inactivo.backgroundColor, const Color(0xFF102532));
     });
   });
+
+  group('Issue 3 (feedback-pruebas): spacing tiers', () {
+    testWidgets('the header title sits at title-tier inset (20px) -- '
+        'ReorderableListView.padding used to double up on top of '
+        "PluriRootHeader's own internal inset", (tester) async {
+      setLargeSurface(tester);
+      _suppressListTileInkAssertion();
+      final estado = await crearEstadoConFavoritos();
+      addTearDown(estado.dispose);
+      final l10n = lookupAppLocalizations(const Locale('en'));
+
+      await tester.pumpWidget(buildScreen(estado));
+      await pumpStable(tester);
+
+      final titulo = find.descendant(
+        of: find.byType(PluriRootHeader),
+        matching: find.text(l10n.favoritesTitle),
+      );
+      expect(
+        tester.getTopLeft(titulo).dx,
+        PluriLayout.titleHorizontal,
+        reason:
+            'PluriRootHeader already supplies its own 20px inset; the '
+            'previous ReorderableListView.padding of 16 doubled up on top '
+            'of it, landing the title at 36px instead of 20px -- the ONE '
+            "root screen whose header didn't match Alarmas/Ajustes",
+      );
+    });
+
+    testWidgets(
+      'the header sits at the SAME horizontal position whether the list is '
+      'empty or populated -- two mutually-exclusive states of the same '
+      'header must not read differently',
+      (tester) async {
+        setLargeSurface(tester);
+        final l10n = lookupAppLocalizations(const Locale('en'));
+
+        final vacio = await crearEstadoVacio();
+        addTearDown(vacio.dispose);
+        await tester.pumpWidget(buildScreen(vacio));
+        await pumpStable(tester);
+        final dxVacio =
+            tester
+                .getTopLeft(
+                  find.descendant(
+                    of: find.byType(PluriRootHeader),
+                    matching: find.text(l10n.favoritesTitle),
+                  ),
+                )
+                .dx;
+
+        _suppressListTileInkAssertion();
+        final conFavoritos = await crearEstadoConFavoritos();
+        addTearDown(conFavoritos.dispose);
+        await tester.pumpWidget(buildScreen(conFavoritos));
+        await pumpStable(tester);
+        final dxConFavoritos =
+            tester
+                .getTopLeft(
+                  find.descendant(
+                    of: find.byType(PluriRootHeader),
+                    matching: find.text(l10n.favoritesTitle),
+                  ),
+                )
+                .dx;
+
+        expect(
+          dxConFavoritos,
+          dxVacio,
+          reason:
+              'the empty and populated branches of this screen must render '
+              'the SAME header inset -- they previously did not (0 vs 16 '
+              'extra px of list-level padding)',
+        );
+      },
+    );
+
+    testWidgets(
+      'each favourite row uses row-tier horizontal inset (12), not the '
+      'card-tier constant a background-less row was never meant to carry',
+      (tester) async {
+        setLargeSurface(tester);
+        _suppressListTileInkAssertion();
+        final estado = await crearEstadoConFavoritos();
+        addTearDown(estado.dispose);
+
+        await tester.pumpWidget(buildScreen(estado));
+        await pumpStable(tester);
+
+        expect(
+          tester.getTopLeft(find.byType(FilaEmisoraPlana).first).dx,
+          PluriLayout.rowHorizontal,
+          reason:
+              'audit 4.3: background-less rows are row tier (12), matching '
+              'the same widget already fixed on Buscar -- not card tier '
+              '(16)',
+        );
+      },
+    );
+  });
 }
 
 void setLargeSurface(WidgetTester tester) {