fix(favoritos): restyle the dashed custom-station CTA to spec

Tier 4 visual fidelity, audit 4.5 (t4 line 235): the border and the
label/icon now use the prototype's two DIFFERENT opacities
(rgba(255,255,255,.16) stroke vs rgba(242,247,250,.6) text/icon,
previously one shared 50% colour for both), padding is a uniform 14
instead of symmetric(18,16), and the icon is a plain add glyph at 20px
instead of add_circle_outline_rounded.

test/pantallas/pantalla_favoritos_test.dart

@@ -102,6 +102,33 @@ void main() {
     await tester.pump(const Duration(milliseconds: 100));
   }
 
+  group('visual fidelity (audit 4.5): dashed custom-station CTA', () {
+    testWidgets(
+      'padding is 14 all around, the icon is a plain add glyph at 20px, '
+      'and the label is 13.5px/w800 (t4 line 235)',
+      (tester) async {
+        final estado = await crearEstadoVacio();
+        addTearDown(estado.dispose);
+        await tester.pumpWidget(buildScreen(estado));
+        await pumpStable(tester);
+
+        final padding = tester.widget<Padding>(
+          find.byKey(const Key('custom-station-cta-padding')),
+        );
+        expect(padding.padding, const EdgeInsets.all(14));
+
+        expect(find.byIcon(Icons.add_circle_outline_rounded), findsNothing);
+        final icon = tester.widget<Icon>(find.byIcon(Icons.add_rounded));
+        expect(icon.size, 20);
+
+        final l10n = lookupAppLocalizations(const Locale('en'));
+        final texto = tester.widget<Text>(find.text(l10n.customStationsAddCta));
+        expect(texto.style?.fontSize, 13.5);
+        expect(texto.style?.fontWeight, FontWeight.w800);
+      },
+    );
+  });
+
   // ── EstadoRadio: new state surface (state-layer, not widget-layer) ───────
 
   test('listaFavoritosManual returns favorites in stored order, NOT re-sorted '