fix(conversation): add missing token columns to MessageEntity

Add input_tokens and output_tokens columns that evolution-service
defines to prevent synchronize:true from trying to drop them.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/services/conversation-service/src/domain/entities/message.entity.ts

@@ -54,6 +54,14 @@ export class MessageEntity {
   @Column({ type: 'jsonb', nullable: true })
   metadata: Record<string, unknown>;
 
+  // ========== Token统计字段（与evolution-service保持一致）==========
+
+  @Column({ name: 'input_tokens', default: 0 })
+  inputTokens: number;
+
+  @Column({ name: 'output_tokens', default: 0 })
+  outputTokens: number;
+
   @CreateDateColumn({ name: 'created_at' })
   createdAt: Date;