feat(android): share podcast playback and foreground broadcasting

Add native Camera2 capture, MPEG-TS segmentation and foreground service with notification stop. Reuse shared authenticated uploads and replay finalization, add capture regression tests and document platform limitations. Update Avalonia to 12.1.4.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/PostIt/PostIt.Android/Services/PodcastCaptureService.cs

@@ -0,0 +1,109 @@
+using System;
+using System.Runtime.Versioning;
+using System.Threading;
+using System.Threading.Tasks;
+using Android.App;
+using Android.Content;
+using Android.Content.PM;
+using Android.OS;
+using AndroidX.Core.App;
+
+namespace PostIt.Android.Services;
+
+[Service(Exported = false, ForegroundServiceType = ForegroundService.TypeCamera | ForegroundService.TypeMicrophone)]
+[SupportedOSPlatform("android26.0")]
+public sealed class PodcastCaptureService : Service
+{
+    private const string Channel = "podcast-broadcast";
+    internal const string StopAction = "fr.pschneider.postit.STOP_PODCAST";
+    private const int NotificationId = 4044;
+    private static TaskCompletionSource<PodcastCaptureService>? _pending;
+    private PowerManager.WakeLock? _wakeLock;
+    internal AndroidPodcastCapture? Capture { get; set; }
+
+    public static async Task<PodcastCaptureService> StartAsync(Activity activity, bool microphone, CancellationToken ct)
+    {
+        if (_pending is not null) throw new InvalidOperationException("Un direct Android est deja en cours.");
+        var pending = new TaskCompletionSource<PodcastCaptureService>(TaskCreationOptions.RunContinuationsAsynchronously);
+        _pending = pending;
+        try
+        {
+            var intent = new Intent(activity, typeof(PodcastCaptureService)).PutExtra("microphone", microphone);
+            activity.StartForegroundService(intent);
+            return await pending.Task.WaitAsync(TimeSpan.FromSeconds(10), ct);
+        }
+        catch
+        {
+            activity.StopService(new Intent(activity, typeof(PodcastCaptureService)));
+            _pending = null;
+            throw;
+        }
+    }
+
+    public override StartCommandResult OnStartCommand(Intent? intent, StartCommandFlags flags, int startId)
+    {
+        if (intent?.Action == StopAction)
+        {
+            if (Capture is { } capture) capture.RequestStop();
+            else
+            {
+                _pending?.TrySetException(new System.OperationCanceledException("Demarrage du direct annule depuis la notification."));
+                StopSelf();
+            }
+            return StartCommandResult.NotSticky;
+        }
+        try
+        {
+            var manager = GetSystemService(NotificationService) as NotificationManager
+                ?? throw new InvalidOperationException("Notifications Android indisponibles.");
+            manager.CreateNotificationChannel(new NotificationChannel(Channel, "Diffusion podcast", NotificationImportance.Low));
+            var launch = PackageManager?.GetLaunchIntentForPackage(PackageName!)
+                ?? throw new InvalidOperationException("Application Android indisponible.");
+            var open = PendingIntent.GetActivity(this, 0, launch, PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable);
+            var stop = PendingIntent.GetService(this, 1,
+                new Intent(this, typeof(PodcastCaptureService)).SetAction(StopAction),
+                PendingIntentFlags.UpdateCurrent | PendingIntentFlags.Immutable);
+            var builder = new NotificationCompat.Builder(this, Channel);
+            builder.SetSmallIcon(global::Android.Resource.Drawable.IcMenuCamera);
+            builder.SetContentTitle("Podcast en direct");
+            builder.SetContentText("Camera active. Toucher pour revenir au direct.");
+            builder.SetContentIntent(open);
+            builder.SetOngoing(true);
+            builder.AddAction(global::Android.Resource.Drawable.IcMediaPause, "Arreter et publier", stop);
+            var notification = builder.Build();
+            var type = (ForegroundService)0;
+            if (OperatingSystem.IsAndroidVersionAtLeast(30))
+            {
+                type = ForegroundService.TypeCamera;
+                if (intent?.GetBooleanExtra("microphone", false) == true) type |= ForegroundService.TypeMicrophone;
+            }
+            ServiceCompat.StartForeground(this, NotificationId, notification, (int)type);
+            var power = GetSystemService(PowerService) as PowerManager
+                ?? throw new InvalidOperationException("Gestion d'alimentation Android indisponible.");
+            _wakeLock = power.NewWakeLock(WakeLockFlags.Partial, "PostIt:Podcast")
+                ?? throw new InvalidOperationException("Le verrou d'alimentation Android est indisponible.");
+            _wakeLock.Acquire();
+            _pending?.TrySetResult(this);
+        }
+        catch (Exception ex)
+        {
+            _pending?.TrySetException(ex);
+            StopSelf();
+        }
+        return StartCommandResult.NotSticky;
+    }
+
+    public override IBinder? OnBind(Intent? intent) => null;
+
+    public override void OnDestroy()
+    {
+        _pending?.TrySetException(new InvalidOperationException("Le service de diffusion Android a ete arrete."));
+        Capture?.RequestStop();
+        Capture = null;
+        if (_wakeLock?.IsHeld == true) _wakeLock.Release();
+        _wakeLock?.Dispose();
+        _wakeLock = null;
+        _pending = null;
+        base.OnDestroy();
+    }
+}