refactor: improve session handling and validation in N8n integration

This commit enhances the N8n integration by refining session management and validation logic. Key changes include:
- Added error handling for session creation failures in the BaseChatbotService.
- Removed unused methods and properties in N8nService and N8nDto to streamline the codebase.
- Updated N8n schema to enforce required fields and improve validation checks.
- Simplified message processing logic to utilize base class methods, enhancing maintainability.

These improvements contribute to a more robust and efficient N8n integration.

src/api/integrations/chatbot/n8n/dto/n8n.dto.ts

@@ -1,5 +1,3 @@
-import { TriggerOperator, TriggerType } from '@prisma/client';
-
 import { BaseChatbotDto, BaseChatbotSettingDto } from '../../base-chatbot.dto';
 
 export class N8nDto extends BaseChatbotDto {
@@ -7,26 +5,10 @@ export class N8nDto extends BaseChatbotDto {
   webhookUrl?: string;
   basicAuthUser?: string;
   basicAuthPass?: string;
-
-  // Advanced bot properties (copied from DifyDto style)
-  triggerType: TriggerType;
-  triggerOperator?: TriggerOperator;
-  triggerValue?: string;
-  expire?: number;
-  keywordFinish?: string;
-  delayMessage?: number;
-  unknownMessage?: string;
-  listeningFromMe?: boolean;
-  stopBotFromMe?: boolean;
-  keepOpen?: boolean;
-  debounceTime?: number;
-  ignoreJids?: string[];
-  splitMessages?: boolean;
-  timePerChar?: number;
 }
 
 export class N8nSettingDto extends BaseChatbotSettingDto {
-  // N8n specific fields
+  // N8n has no specific fields
 }
 
 export class N8nMessageDto {