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/AndroidVideoSurface.cs

@@ -0,0 +1,37 @@
+using System;
+using Avalonia.Android;
+using Avalonia.Controls;
+using Avalonia.Platform;
+using LibVLCSharp.Shared;
+using VideoView = LibVLCSharp.Platforms.Android.VideoView;
+
+namespace PostIt.Android.Services;
+
+internal sealed class AndroidVideoSurface(MediaPlayer player) : NativeControlHost, IDisposable
+{
+    private VideoView? _video;
+    private bool _disposed;
+
+    protected override IPlatformHandle CreateNativeControlCore(IPlatformHandle parent)
+    {
+        var activity = MainActivity.Current
+            ?? throw new InvalidOperationException("L'activite Android est indisponible.");
+        var video = new VideoView(activity) { MediaPlayer = _disposed ? null : player };
+        _video = video;
+        return new AndroidViewControlHandle(video);
+    }
+
+    protected override void DestroyNativeControlCore(IPlatformHandle control)
+    {
+        if (control is AndroidViewControlHandle { View: VideoView video })
+            video.MediaPlayer = null;
+        _video = null;
+        base.DestroyNativeControlCore(control);
+    }
+
+    public void Dispose()
+    {
+        _disposed = true;
+        if (_video is not null) _video.MediaPlayer = null;
+    }
+}