Added Requesty as a provider

Requesty is an OpenAI compatible AI gateway. The provider mirrors OpenRouter: chat completions over https://router.requesty.ai/v1/, the same project headers, and a model list read from both the managed policies (models/managed) and the full catalog (models), including the context window.

app/MindWork AI Studio/Provider/Requesty/RequestyModel.cs

@@ -0,0 +1,10 @@
+using System.Text.Json.Serialization;
+
+namespace AIStudio.Provider.Requesty;
+
+/// <summary>
+/// A data model for a Requesty model from the API.
+/// </summary>
+/// <param name="Id">The model's ID.</param>
+/// <param name="ContextWindowTokens">How much the model reads and writes in one conversation, in tokens.</param>
+public readonly record struct RequestyModel(string Id, [property: JsonPropertyName("context_window")] int? ContextWindowTokens);