AutoCommit: Bool → Dropdown (mention/enforce/forbid), leerer System-Prompt fix

Endpoints/ChatEndpoint.cs

@@ -146,10 +146,9 @@ public static class ChatEndpoint
             }, attachmentRecords);
         }
 
-        var systemPrompt = new List<object>
-        {
-            new { type = "text", text = systemPromptText }
-        };
+        var systemPrompt = string.IsNullOrWhiteSpace(systemPromptText)
+            ? new List<object>()
+            : new List<object> { new { type = "text", text = systemPromptText } };
 
         var workspace = session.Workspace;
         if (!string.IsNullOrEmpty(workspace))