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.

lib/pantallas/pantalla_favoritos.dart

@@ -474,24 +474,37 @@ class _CtaEmisoraPersonalizada extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final l10n = AppLocalizations.of(context);
-    final color = Theme.of(
+    // Audit 4.5 (t4 line 235): the border and the label/icon are TWO
+    // different opacities in the prototype — `rgba(255,255,255,.16)` for
+    // the dashed stroke, `rgba(242,247,250,.6)` for the text/icon — not one
+    // shared 50% colour for both.
+    final colorBorde = Colors.white.withValues(alpha: 0.16);
+    final colorTexto = Theme.of(
       context,
-    ).colorScheme.onSurface.withValues(alpha: 0.5);
+    ).colorScheme.onSurface.withValues(alpha: 0.6);
     return CustomPaint(
-      painter: _DashedBorderPainter(color: color),
+      painter: _DashedBorderPainter(color: colorBorde),
       child: Material(
         color: Colors.transparent,
         child: InkWell(
           borderRadius: BorderRadius.circular(16),
           onTap: onTap,
           child: Padding(
-            padding: const EdgeInsets.symmetric(vertical: 18, horizontal: 16),
+            key: const Key('custom-station-cta-padding'),
+            padding: const EdgeInsets.all(14),
             child: Row(
               mainAxisAlignment: MainAxisAlignment.center,
               children: [
-                Icon(Icons.add_circle_outline_rounded, color: color),
+                Icon(Icons.add_rounded, size: 20, color: colorTexto),
                 const SizedBox(width: 8),
-                Text(l10n.customStationsAddCta, style: TextStyle(color: color)),
+                Text(
+                  l10n.customStationsAddCta,
+                  style: TextStyle(
+                    fontSize: 13.5,
+                    fontWeight: FontWeight.w800,
+                    color: colorTexto,
+                  ),
+                ),
               ],
             ),
           ),

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 '