Added the visual briefing assistant (#893)

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

@@ -0,0 +1,34 @@
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Assistants.VisualBriefing;
+
+/// <summary>
+/// Stores an immutable validated plan-stage artifact.
+/// </summary>
+[JsonUnmappedMemberHandling(JsonUnmappedMemberHandling.Disallow)]
+public sealed class VisualBriefingPlanArtifact
+{
+    /// <summary>Gets or sets the intermediate artifact schema version.</summary>
+    public int ArtifactVersion { get; set; } = VisualBriefingVersions.INTERMEDIATE_ARTIFACT;
+    
+    /// <summary>Gets or sets the plan prompt contract version.</summary>
+    public int ContractVersion { get; set; } = VisualBriefingVersions.PLAN_CONTRACT;
+    
+    /// <summary>Gets or sets the immutable artifact identifier.</summary>
+    public Guid ArtifactId { get; init; }
+    
+    /// <summary>Gets or sets the artifact creation time.</summary>
+    public DateTimeOffset CreatedAtUtc { get; set; }
+    
+    /// <summary>Gets or sets the hash of the artifact payload.</summary>
+    public string PayloadHash { get; init; } = string.Empty;
+    
+    /// <summary>Gets or sets the ordered planned sections.</summary>
+    public List<VisualBriefingPlanSection> Sections { get; init; } = [];
+    
+    /// <summary>Gets or sets the canonical structural signature.</summary>
+    public string StructuralSignature { get; init; } = string.Empty;
+    
+    /// <summary>Gets or sets the contributing model name.</summary>
+    public string Model { get; init; } = string.Empty;
+}