Brand logo: one locked image layer per scene above the background, image from App Settings

- Source.IsBrandLogo persisted (additive migration); layer healed on load, removal blocked
- Image stored as an asset; settings keep the asset id and file name
- App Settings: Brand Logo file field with Browse
- Default placement top-left; per-scene eye uses the existing element visibility
Test: BrandLogoTests; layout/background tests pass (34). Not pushed.

Services/LayoutStore.Save.cs

@@ -92,7 +92,7 @@ public partial class LayoutStore : IDisposable
                                     ChatShowTimestamps, ChatShowBadges, ChatMemberColor, ChatSuperChatColor,
                                     WebUri, MediaPath, MediaIsLooping, MediaVolume, MediaPlaybackState,
                                     AlertVideoAssetId, AlertVideoPath, AlertUseDefaultVideo, AlertShowTicker, AlertVideoVolume,
-                                    AlertDisplayMethod)
+                                    AlertDisplayMethod, IsBrandLogo)
                 VALUES ($id, $sceneId, $assetId, $type, $name, $isEnabled,
                         $x, $y, $w, $h, $opacity, $monitor,
                         $clip, $mirrored, $isBackground, $captureKey, $showDesktop, $sort,
@@ -100,7 +100,7 @@ public partial class LayoutStore : IDisposable
                         $chatTimestamps, $chatBadges, $chatMemberColor, $chatSuperChatColor,
                         $webUri, $mediaPath, $mediaIsLooping, $mediaVolume, $mediaPlaybackState,
                         $alertVideoAssetId, $alertVideoPath, $alertUseDefaultVideo, $alertShowTicker, $alertVideoVolume,
-                        $alertDisplayMethod)
+                        $alertDisplayMethod, $isBrandLogo)
                 """;
             cmd.Transaction = tx;
             var idP = cmd.Parameters.Add("$id", SqliteType.Text);
@@ -140,6 +140,7 @@ public partial class LayoutStore : IDisposable
             var alertShowTickerP = cmd.Parameters.Add("$alertShowTicker", SqliteType.Integer);
             var alertVideoVolumeP = cmd.Parameters.Add("$alertVideoVolume", SqliteType.Real);
             var alertDisplayMethodP = cmd.Parameters.Add("$alertDisplayMethod", SqliteType.Integer);
+            var isBrandLogoP = cmd.Parameters.Add("$isBrandLogo", SqliteType.Integer);
 
             // Source and WebcamSceneConfig share ONE z-order space per scene:
             // each element gets its index within scene.Elements regardless of
@@ -188,6 +189,7 @@ public partial class LayoutStore : IDisposable
                     alertShowTickerP.Value = source.AlertShowTicker ? 1 : 0;
                     alertVideoVolumeP.Value = source.AlertVideoVolume;
                     alertDisplayMethodP.Value = (int)source.AlertDisplayMethod;
+                    isBrandLogoP.Value = source.IsBrandLogo ? 1 : 0;
                     cmd.ExecuteNonQuery();
                 }
             }