Add per-answer thinking disclosure

app/MindWork AI Studio/Provider/Perplexity/Delta.cs

@@ -1,7 +1,17 @@
+using System.Text.Json;
+
+using AIStudio.Provider.OpenAI;
+
 namespace AIStudio.Provider.Perplexity;
 
 /// <summary>
 /// The delta text of a choice.
 /// </summary>
 /// <param name="Content">The content of the delta text.</param>
-public readonly record struct Delta(string Content);
+/// <param name="ReasoningContent">OpenAI-compatible reasoning content.</param>
+/// <param name="Reasoning">OpenRouter-compatible reasoning content.</param>
+/// <param name="ReasoningDetails">Structured reasoning details.</param>
+public readonly record struct Delta(string Content, string? ReasoningContent, string? Reasoning, IList<JsonElement>? ReasoningDetails)
+{
+    public string Thinking => ThinkingContent.Get(this.ReasoningContent, this.Reasoning, this.ReasoningDetails);
+}