Generated the JSON contracts of visual briefings and model answers at compile time (#1151)

app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingAssetMetadata.cs

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+namespace AIStudio.Assistants.VisualBriefing;
+
+/// <summary>
+/// What the protected data of an exported briefing tells about one of its pictures.
+/// </summary>
+/// <param name="Description">What the picture shows.</param>
+/// <param name="AltText">The text for people who cannot see the picture.</param>
+internal sealed record VisualBriefingAssetMetadata(string Description, string AltText);