App: scelta canale YouTube MLTV/società, privacy e condivisione link.

Premium Full può forzare il canale piattaforma; visibilità non in elenco o privato;
share_url unificato per Match Live TV e YouTube.

Co-authored-by: Cursor <cursoragent@cursor.com>

mobile/lib/shared/api_client.dart

@@ -153,6 +153,7 @@ class ApiClient {
   Future<StreamSession> createSession(
     String matchId, {
     String platform = 'matchlivetv',
+    String? youtubeChannel,
     String privacyStatus = 'unlisted',
     String qualityPreset = '720p_30_2.5mbps',
     int? targetBitrate,
@@ -164,6 +165,7 @@ class ApiClient {
         'platform': platform,
         'privacy_status': privacyStatus,
         'quality_preset': qualityPreset,
+        if (youtubeChannel != null) 'youtube_channel': youtubeChannel,
         if (targetBitrate != null) 'target_bitrate': targetBitrate,
         if (targetFps != null) 'target_fps': targetFps,
       },