feat(api): REST endpoints for decos, deco groups, playout default deco (#144 S3 (#162))

Adds DecoController (groups + decos CRUD + full-state PUT), playlist and
artist/multi-collection search picker wrappers, a PlaylistController for the
break-content playlist cascade, and PUT /api/playouts/{id}/deco. Fixes the
CreateDecoHandler missing deco-group existence check (FK 500 -> 422), matching
the CreateBlock/CreateTemplate precedent. ReplaceDecoRequest.ToCommand rejects
Merge on the non-mergeable sections (422).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ErsatzTV.Core/Api/MediaCollections/PlaylistGroupResponseModel.cs

@@ -0,0 +1,4 @@
+#nullable enable
+namespace ErsatzTV.Core.Api.MediaCollections;
+
+public record PlaylistGroupResponseModel(int Id, string Name, int PlaylistCount, bool IsSystem);

ErsatzTV.Core/Api/MediaCollections/PlaylistResponseModel.cs

@@ -0,0 +1,4 @@
+#nullable enable
+namespace ErsatzTV.Core.Api.MediaCollections;
+
+public record PlaylistResponseModel(int Id, int PlaylistGroupId, string Name, bool IsSystem);

ErsatzTV.Core/Api/Scheduling/DecoBreakContentResponseModel.cs

@@ -0,0 +1,17 @@
+#nullable enable
+using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Domain.Scheduling;
+
+namespace ErsatzTV.Core.Api.Scheduling;
+
+public record DecoBreakContentResponseModel(
+    int Id,
+    CollectionType CollectionType,
+    int? CollectionId,
+    int? MediaItemId,
+    int? MultiCollectionId,
+    int? SmartCollectionId,
+    int? PlaylistId,
+    int? PlaylistGroupId,
+    string? SelectionName,
+    DecoBreakPlacement Placement);

ErsatzTV.Core/Api/Scheduling/DecoGroupResponseModel.cs

@@ -0,0 +1,4 @@
+#nullable enable
+namespace ErsatzTV.Core.Api.Scheduling;
+
+public record DecoGroupResponseModel(int Id, string Name, int DecoCount);

ErsatzTV.Core/Api/Scheduling/DecoListItemResponseModel.cs

@@ -0,0 +1,4 @@
+#nullable enable
+namespace ErsatzTV.Core.Api.Scheduling;
+
+public record DecoListItemResponseModel(int Id, int DecoGroupId, string DecoGroupName, string Name);

ErsatzTV.Core/Api/Scheduling/DecoResponseModel.cs

@@ -0,0 +1,34 @@
+#nullable enable
+using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Domain.Scheduling;
+
+namespace ErsatzTV.Core.Api.Scheduling;
+
+public record DecoResponseModel(
+    int Id,
+    int DecoGroupId,
+    string DecoGroupName,
+    string Name,
+    DecoMode WatermarkMode,
+    List<int> WatermarkIds,
+    bool UseWatermarkDuringFiller,
+    DecoMode GraphicsElementsMode,
+    List<int> GraphicsElementIds,
+    bool UseGraphicsElementsDuringFiller,
+    DecoMode BreakContentMode,
+    List<DecoBreakContentResponseModel> BreakContent,
+    DecoMode DefaultFillerMode,
+    CollectionType DefaultFillerCollectionType,
+    int? DefaultFillerCollectionId,
+    int? DefaultFillerMediaItemId,
+    int? DefaultFillerMultiCollectionId,
+    int? DefaultFillerSmartCollectionId,
+    string? DefaultFillerSelectionName,
+    bool DefaultFillerTrimToFit,
+    DecoMode DeadAirFallbackMode,
+    CollectionType DeadAirFallbackCollectionType,
+    int? DeadAirFallbackCollectionId,
+    int? DeadAirFallbackMediaItemId,
+    int? DeadAirFallbackMultiCollectionId,
+    int? DeadAirFallbackSmartCollectionId,
+    string? DeadAirFallbackSelectionName);