feat(connectivity): restyle offline and reconnect banners

Tint the mini player's reconnecting/error sub-states with the
offlineAccent token (added in WU1, unused until now): the status
label, the reconnect spinner, and the error retry icon now read as
visually distinct "connectivity trouble" states instead of blending
into the ordinary loading/paused look. Plain buffering keeps the
default colour, confirmed by a dedicated regression test.

Verify-first gate (task 16.1): ControladorReconexion.intentos exists,
but ServicioAudio never surfaces it past a debug log line, and its
estadoStream only carries the EstadoReproduccion enum. Adding an
attempt-count label would require a getter/stream on
servicio_audio.dart, one of the files this change must keep at an
empty diff against main. Ship the restyle without the counter, per
the risk register's own fallback.

WU16.

lib/widgets/mini_reproductor.dart

@@ -129,20 +129,31 @@ class _MiniReproductorState extends State<MiniReproductor> {
                                           EstadoReproduccion.detenido;
                                       final activo =
                                           s == EstadoReproduccion.reproduciendo;
+                                      // WU16: reconectando/error are
+                                      // "connectivity trouble" states —
+                                      // tinted with offlineAccent so they
+                                      // read as visually distinct from
+                                      // ordinary loading/paused/stopped.
+                                      final conexionEnProblema =
+                                          s ==
+                                              EstadoReproduccion.reconectando ||
+                                          s == EstadoReproduccion.error;
                                       return Text(
                                         _labelEstado(l10n, s),
                                         style: Theme.of(
                                           context,
                                         ).textTheme.bodySmall?.copyWith(
                                           color:
-                                              activo
+                                              conexionEnProblema
+                                                  ? t.offlineAccent
+                                                  : activo
                                                   ? t.warmCoral
                                                   : Theme.of(context)
                                                       .colorScheme
                                                       .onSurface
                                                       .withValues(alpha: 0.7),
                                           fontWeight:
-                                              activo
+                                              (activo || conexionEnProblema)
                                                   ? FontWeight.w600
                                                   : FontWeight.w400,
                                         ),
@@ -173,12 +184,20 @@ class _MiniReproductorState extends State<MiniReproductor> {
                   // cargando (spinner), never as the error/retry affordance.
                   if (s == EstadoReproduccion.cargando ||
                       s == EstadoReproduccion.reconectando) {
-                    return const SizedBox(
+                    // WU16: only the reconectando sub-state gets the offline
+                    // accent — plain cargando (e.g. the very first play)
+                    // keeps the default spinner colour, since it is not a
+                    // connectivity problem.
+                    final reconectando = s == EstadoReproduccion.reconectando;
+                    return SizedBox(
                       width: 48,
                       height: 48,
                       child: Padding(
-                        padding: EdgeInsets.all(12),
-                        child: CircularProgressIndicator(strokeWidth: 2),
+                        padding: const EdgeInsets.all(12),
+                        child: CircularProgressIndicator(
+                          strokeWidth: 2,
+                          color: reconectando ? t.offlineAccent : null,
+                        ),
                       ),
                     );
                   }
@@ -187,7 +206,7 @@ class _MiniReproductorState extends State<MiniReproductor> {
                     final emisoraActual = estado.emisoraActual;
                     return IconButton(
                       tooltip: l10n.retryAction,
-                      icon: const Icon(Icons.refresh_rounded),
+                      icon: Icon(Icons.refresh_rounded, color: t.offlineAccent),
                       onPressed:
                           emisoraActual != null
                               ? () => estado.reproducir(emisoraActual)