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.Load.cs

@@ -102,7 +102,7 @@ public partial class LayoutStore : IDisposable
                        ChatShowTimestamps, ChatShowBadges, ChatMemberColor, ChatSuperChatColor,
                        WebUri, MediaPath, MediaIsLooping, MediaVolume, MediaPlaybackState,
                        AlertVideoAssetId, AlertVideoPath, AlertUseDefaultVideo, AlertShowTicker, AlertVideoVolume, SortOrder,
-                       AlertDisplayMethod
+                       AlertDisplayMethod, IsBrandLogo
                 FROM Source ORDER BY SortOrder
                 """;
             using var reader = cmd.ExecuteReader();
@@ -154,6 +154,7 @@ public partial class LayoutStore : IDisposable
                     AlertShowTicker = reader.IsDBNull(33) ? true : reader.GetInt32(33) != 0,
                     AlertVideoVolume = reader.IsDBNull(34) ? 1.0 : reader.GetDouble(34),
                     AlertDisplayMethod = reader.IsDBNull(36) ? AlertDisplayMethod.TickerScroll : (AlertDisplayMethod)reader.GetInt32(36),
+                    IsBrandLogo = reader.GetInt32(reader.GetOrdinal("IsBrandLogo")) != 0,
                 };
                 if (!sourcesByScene.TryGetValue(sceneId, out var list))
                     sourcesByScene[sceneId] = list = new List<(Source, int)>();