wip: partial implementation salvaged from interrupted workflow run

Untrusted draft — no build/test had run yet. Review before building on it.

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

ErsatzTV.Core/Api/Filler/FillerPresetResponseModel.cs

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+namespace ErsatzTV.Core.Api.Filler;
+
+public record FillerPresetResponseModel(int Id, string Name);

ErsatzTV.Core/Api/Graphics/GraphicsElementResponseModel.cs

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+namespace ErsatzTV.Core.Api.Graphics;
+
+public record GraphicsElementResponseModel(int Id, string Name);

ErsatzTV.Core/Api/Watermarks/WatermarkResponseModel.cs

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+namespace ErsatzTV.Core.Api.Watermarks;
+
+public record WatermarkResponseModel(int Id, string Name);