fix typo

Author: Jicheng Lu

src/Infrastructure/BotSharp.Core/Files/Services/Instruct/FileInstructService.SelectFile.cs

@@ -80,6 +80,10 @@ private async Task<IEnumerable<MessageFileModel>> SelectFiles(IEnumerable<Messag
         {
             return res;
         }
+        else if (files.Count() == 1)
+        {
+            return files;
+        }
 
         var agentService = _services.GetRequiredService<IAgentService>();
         var llmProviderService = _services.GetRequiredService<ILlmProviderService>();
@@ -115,7 +119,7 @@ private async Task<IEnumerable<MessageFileModel>> SelectFiles(IEnumerable<Messag
             }).ToList();
 
             var agentId = !string.IsNullOrWhiteSpace(options.AgentId) ? options.AgentId : BuiltInAgentId.FileAssistant;
-            var template = !string.IsNullOrWhiteSpace(options.Template) ? options.Template : "select_chat_file_instruction";
+            var template = !string.IsNullOrWhiteSpace(options.Template) ? options.Template : "select-chat-file_instruction";
             var prompt = db.GetAgentTemplate(agentId, template);
 
             var data = new Dictionary<string, object>