feat(streaming): buffer resilience and automatic reconnection

- Construct the audio player with an enlarged live-stream buffer (15-50s forward cushion, 2.5s to start, 5s after rebuffer) so short network drops play through silently
- Add reconnect-on-stall state machine with bounded exponential backoff (1/2/4/8/16s, ~90s total window, 5 attempts) that re-prepares to the live edge; backoff/decision logic extracted to controlador_reconexion.dart as pure testable code
- Surface a new reconnecting playback state in the mini player and full player (localized in all 13 locales) instead of error dialogs during the retry window; a single friendly error appears only after exhaustion
- Guard interplay: user pause/stop cancels retries, audio interruptions cancel reconnect, alarm wake-up path keeps precedence, recording fails cleanly during drops
- Reset retry budget on station change; route stream timeouts through the network-error class
- 10 new tests (99 total green), flutter analyze clean

lib/pantallas/pantalla_alarma_sonando.dart

@@ -64,6 +64,11 @@ class _PantallaAlarmaSonandoState extends State<PantallaAlarmaSonando> {
     }
     _iniciarFadeIn();
 
+    // S7-R4 boundary: only `reproduciendo` cancels the fallback timer —
+    // `reconectando`/`cargando` do NOT count as playing, so the 12-second
+    // fallback below stays authoritative during the alarm ring. Waking the
+    // user reliably beats reconnect persistence: if the radio is still
+    // retrying when the timer fires, the bundled WAV takes over.
     _estadoSub = radio.estadoStream.listen((estado) {
       if (estado == EstadoReproduccion.reproduciendo && mounted) {
         _fallbackTimer?.cancel();

lib/pantallas/pantalla_reproductor.dart

@@ -217,7 +217,10 @@ class _WaveHero extends StatelessWidget {
       stream: estadoStream,
       builder: (context, snapshot) {
         final reproduciendo = snapshot.data == EstadoReproduccion.reproduciendo;
-        final cargando = snapshot.data == EstadoReproduccion.cargando;
+        // S7-R3: reconectando renders as loading, never as error.
+        final cargando =
+            snapshot.data == EstadoReproduccion.cargando ||
+            snapshot.data == EstadoReproduccion.reconectando;
         final hayError = snapshot.data == EstadoReproduccion.error;
 
         return SizedBox(
@@ -506,9 +509,9 @@ class _GrabacionWidget extends StatelessWidget {
                                 ? AppLocalizations.of(
                                   ctx,
                                 ).durationMinutesOnly(opcion.duracion.inMinutes)
-                                : AppLocalizations.of(
-                                  ctx,
-                                ).durationSecondsOnly(opcion.duracion.inSeconds),
+                                : AppLocalizations.of(ctx).durationSecondsOnly(
+                                  opcion.duracion.inSeconds,
+                                ),
                           ),
                           onPressed: () {
                             estado.iniciarGrabacion(duracion: opcion.duracion);
@@ -651,7 +654,10 @@ class _Controles extends StatelessWidget {
       builder: (context, snapshot) {
         final s = snapshot.data ?? EstadoReproduccion.detenido;
         final reproduciendo = s == EstadoReproduccion.reproduciendo;
-        final cargando = s == EstadoReproduccion.cargando;
+        // S7-R3: reconectando shows the loading spinner, not the error column.
+        final cargando =
+            s == EstadoReproduccion.cargando ||
+            s == EstadoReproduccion.reconectando;
         final hayError = s == EstadoReproduccion.error;
 
         if (hayError) {
@@ -808,11 +814,9 @@ class _TimerWidget extends StatelessWidget {
         final s = t.inSeconds.remainder(60).toString().padLeft(2, '0');
         final label =
             t.inHours > 0
-                ? AppLocalizations.of(context).durationHoursMinutesSeconds(
-                  t.inHours,
-                  m,
-                  s,
-                )
+                ? AppLocalizations.of(
+                  context,
+                ).durationHoursMinutesSeconds(t.inHours, m, s)
                 : AppLocalizations.of(context).durationMinutesSeconds(m, s);
 
         return Row(