Added local RAG (#756)

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

app/MindWork AI Studio/Tools/Validation/ProviderValidation.cs

@@ -22,6 +22,7 @@ public sealed class ProviderValidation
 
     public Func<bool> IsModelProvidedManually { get; init; } = () => false;
 
+    public Func<string> GetCustomTokenizerValidationIssue { get; init; } = () => string.Empty;
     public Func<bool> IsModelSelectionHidden { get; init; } = () => false;
 
     public string? ValidatingHostname(string hostname)
@@ -132,6 +133,15 @@ public sealed class ProviderValidation
         return null;
     }
 
+    public string? ValidatingCustomTokenizer(string _)
+    {
+        var issue = this.GetCustomTokenizerValidationIssue();
+        if (string.IsNullOrWhiteSpace(issue))
+            return null;
+
+        return issue;
+    }
+
     /// <summary>
     /// Validates the Hugging Face inference provider chosen for embeddings.
     /// </summary>
@@ -179,4 +189,4 @@ public sealed class ProviderValidation
 
         return null;
     }
-}
+}