TASK 21 Increment A: media-source model + persistence (schema migration + round-trip test)

SourceType.MediaSource added; MediaSourceType (Video/Audio) and MediaPlaybackState
(Stopped/Playing/Paused) enums. Source gains MediaPath, MediaIsLooping, MediaVolume
(0-1 clamped), MediaPlaybackState. LayoutStore: MigrateSourceTable adds 4 guarded
ALTERs (MediaPath, MediaIsLooping, MediaVolume, MediaPlaybackState); SELECT appends
indices 26-29, INSERT adds 4 columns + params. Round-trip test
MediaSource_Config_Survives_Save_And_Reload passes. Build 0 warnings, 245/247
tests (2 known pre-existing). Gated on creator run for later integration (ffmpeg).

ytLive.Tests/LayoutStorePersistenceTests.cs

@@ -388,4 +388,47 @@ public class LayoutStorePersistenceTests
             try { File.Delete(path); } catch { /* best-effort cleanup */ }
         }
     }
+
+    // TASK 21: media-source config (Path, Looping, Volume, PlaybackState) must
+    // survive a save + reload through the full DELETE-all/re-insert cycle.
+    [Fact]
+    public void MediaSource_Config_Survives_Save_And_Reload()
+    {
+        var path = Path.Combine(Path.GetTempPath(), $"ytLlive-layout-{Guid.NewGuid():N}.db");
+        try
+        {
+            using var store = new LayoutStore(path);
+            var scene = new Scene { Name = "Starting" };
+            var source = new Source
+            {
+                Name = "Starting Loop",
+                Type = SourceType.MediaSource,
+                Width = 1920,
+                Height = 1080,
+                MediaPath = @"C:\videos\starting.mp4",
+                MediaIsLooping = true,
+                MediaVolume = 0.75,
+                MediaPlaybackState = MediaPlaybackState.Playing,
+            };
+            scene.Elements.Add(source);
+
+            store.Save(new[] { scene }, null, null);
+
+            var reloaded = store.Load();
+            var loaded = Assert.Single(reloaded[0].Elements);
+            var loadedSource = Assert.IsType<Source>(loaded);
+
+            Assert.Equal(SourceType.MediaSource, loadedSource.Type);
+            Assert.True(loadedSource.IsMediaSource);
+            Assert.Equal(@"C:\videos\starting.mp4", loadedSource.MediaPath);
+            Assert.True(loadedSource.MediaIsLooping);
+            Assert.Equal(0.75, loadedSource.MediaVolume);
+            Assert.Equal(MediaPlaybackState.Playing, loadedSource.MediaPlaybackState);
+        }
+        finally
+        {
+            SqliteConnection.ClearAllPools();
+            try { File.Delete(path); } catch { /* best-effort cleanup */ }
+        }
+    }
 }