Move the model kinds into the rule engine

app/MindWork AI Studio/Models/Kinds/TextCompletionModelsFamily.cs

@@ -0,0 +1,36 @@
+using AIStudio.Provider;
+
+namespace AIStudio.Models.Kinds;
+
+/// <summary>
+/// The models from before chat completions existed.
+/// </summary>
+/// <remarks>
+/// Providers keep offering some of them -- Helmholtz Blablador still reports text-davinci-003 --
+/// but asking any of them for a chat completion fails. They only answer through the completions
+/// endpoint, which the app does not speak, so they must not stand among the chat models.
+///
+/// "ada" is deliberately not among these names: three letters appear in far too many unrelated ones,
+/// and losing a chat model weighs heavier than keeping a dead one in the list.
+/// </remarks>
+public sealed class TextCompletionModelsFamily : ModelFamily
+{
+    /// <inheritdoc />
+    public override ModelVendor Vendor => ModelVendor.UNKNOWN;
+
+    /// <inheritdoc />
+    public override ModelSource Source => new("https://platform.openai.com/docs/api-reference/completions", new DateOnly(2026, 9, 12), "Ported unchanged from the text completion markers of Provider/ModelKindExtensions.cs.");
+
+    /// <inheritdoc />
+    protected override void Declare(ModelFamilyBuilder builder)
+    {
+        builder.Modifier("davinci").AsSubstring().Kind(ModelKind.TEXT_COMPLETION);
+
+        builder.Modifier("babbage").AsSubstring().Inherits();
+
+        builder.Modifier("curie").AsSubstring().Inherits();
+
+        // The one model of the 3.5 line which never learned to chat, next to the ones which did:
+        builder.Modifier("gpt-3.5-turbo-instruct").AsSegment().Inherits();
+    }
+}