fix(buscar): rebuild the offline banner with offlineAccent

Audit 13.1 (t4 line 641): the banner rendered wifi_off in
colorScheme.error (red) inside a generic glass card. Rebuilt using
offlineAccent (#E8879A) — a token that existed since Tier 1 with no
consumer — for the tint, border and icon, plus the prototype's title/
detail layout and a restyled Retry chip. New offlineBannerTitle key
translated to all 13 locales.

lib/pantallas/pantalla_buscar.dart

@@ -7,6 +7,7 @@ import '../estado/estado_radio.dart';
 import '../l10n/gen/app_localizations.dart';
 import '../modelos/emisora.dart';
 import '../tema/pluri_animate.dart';
+import '../tema/pluriwave_theme.dart';
 import '../widgets/pluri_glass_surface.dart';
 import '../widgets/pluri_icon.dart';
 import '../widgets/pluri_layout.dart';
@@ -847,26 +848,81 @@ class _PantallaBuscarState extends State<PantallaBuscar> {
     );
   }
 
+  // Audit 13.1 (t4 line 641): the prototype's offline banner is a
+  // rgba(207,102,121,X) tinted card — this consolidates on the ONE
+  // `offlineAccent` token (`#E8879A`) the proposal named for this exact
+  // banner (`pluriwave_tokens.dart:77`), which existed unused until now,
+  // rather than introducing a second near-identical raw hex for the tint.
   Widget _errorBanner(
     BuildContext context,
     String error,
     ThemeData theme,
     AppLocalizations l10n,
   ) {
+    final tokens = context.pluriTokens;
     return Padding(
-      padding: const EdgeInsets.all(16),
-      child: PluriGlassSurface(
-        padding: const EdgeInsets.all(12),
-        child: Row(
-          children: [
-            Icon(Icons.wifi_off, color: theme.colorScheme.error),
-            const SizedBox(width: 8),
-            Expanded(child: Text(error)),
-            TextButton(
-              onPressed: () => context.read<EstadoRadio>().cargarPopulares(),
-              child: Text(l10n.retryAction),
-            ),
-          ],
+      padding: const EdgeInsets.symmetric(horizontal: 16),
+      child: DecoratedBox(
+        key: const ValueKey('offline-banner'),
+        decoration: BoxDecoration(
+          color: tokens.offlineAccent.withValues(alpha: 0.14),
+          borderRadius: BorderRadius.circular(16),
+          border: Border.all(
+            color: tokens.offlineAccent.withValues(alpha: 0.4),
+          ),
+        ),
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 15, vertical: 13),
+          child: Row(
+            children: [
+              Icon(Icons.wifi_off, size: 22, color: tokens.offlineAccent),
+              const SizedBox(width: 11),
+              Expanded(
+                child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    Text(
+                      l10n.offlineBannerTitle,
+                      style: const TextStyle(
+                        fontSize: 13.5,
+                        fontWeight: FontWeight.w800,
+                      ),
+                    ),
+                    Text(
+                      error,
+                      style: TextStyle(
+                        fontSize: 11.5,
+                        color: theme.colorScheme.onSurface.withValues(
+                          alpha: 0.65,
+                        ),
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+              const SizedBox(width: 8),
+              TextButton(
+                style: TextButton.styleFrom(
+                  backgroundColor: Colors.white.withValues(alpha: 0.1),
+                  foregroundColor: theme.colorScheme.onSurface,
+                  padding: const EdgeInsets.symmetric(
+                    horizontal: 12,
+                    vertical: 7,
+                  ),
+                  shape: RoundedRectangleBorder(
+                    borderRadius: BorderRadius.circular(10),
+                  ),
+                  textStyle: const TextStyle(
+                    fontSize: 12,
+                    fontWeight: FontWeight.w800,
+                  ),
+                ),
+                onPressed: () => context.read<EstadoRadio>().cargarPopulares(),
+                child: Text(l10n.retryAction),
+              ),
+            ],
+          ),
         ),
       ),
     );