Added a home page prompt for missing API keys of enterprise providers (#1056)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/UserAPIKeys/UserAPIKeyCheckOutcome.cs

@@ -0,0 +1,23 @@
+namespace AIStudio.Tools.UserAPIKeys;
+
+/// <summary>
+/// What a provider says about an API key the user entered.
+/// </summary>
+public enum UserAPIKeyCheckOutcome
+{
+    /// <summary>
+    /// The provider listed its models with the key, so it accepts the key.
+    /// </summary>
+    ACCEPTED,
+
+    /// <summary>
+    /// The provider refused the key. AI Studio does not store it.
+    /// </summary>
+    REJECTED,
+
+    /// <summary>
+    /// Nothing tells whether the provider accepts the key, e.g., because the server was out of reach or the
+    /// provider cannot list its models. AI Studio stores the key anyway.
+    /// </summary>
+    NOT_CHECKED
+}