fix(conversation): add indexes and fix column types to match database

- Add @Index decorators for conversation_id, created_at, role
- Set created_at to timestamptz type to match database
- Set columns nullable to match database schema

This prevents synchronize:true from trying to modify columns
that have dependent indexes.

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

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

@@ -5,6 +5,7 @@ import {
   CreateDateColumn,
   ManyToOne,
   JoinColumn,
+  Index,
 } from 'typeorm';
 import { ConversationEntity } from './conversation.entity';
 
@@ -35,11 +36,14 @@ export const MessageType = {
 export type MessageTypeType = (typeof MessageType)[keyof typeof MessageType];
 
 @Entity('messages')
+@Index('idx_messages_conversation_id', ['conversationId'])
+@Index('idx_messages_created_at', ['createdAt'])
+@Index('idx_messages_role', ['role'])
 export class MessageEntity {
   @PrimaryGeneratedColumn('uuid')
   id: string;
 
-  @Column({ name: 'conversation_id', type: 'uuid' })
+  @Column({ name: 'conversation_id', type: 'uuid', nullable: true })
   conversationId: string;
 
   @Column({ length: 20 })
@@ -56,13 +60,13 @@ export class MessageEntity {
 
   // ========== Token统计字段（与evolution-service保持一致）==========
 
-  @Column({ name: 'input_tokens', default: 0 })
+  @Column({ name: 'input_tokens', nullable: true })
   inputTokens: number;
 
-  @Column({ name: 'output_tokens', default: 0 })
+  @Column({ name: 'output_tokens', nullable: true })
   outputTokens: number;
 
-  @CreateDateColumn({ name: 'created_at' })
+  @CreateDateColumn({ name: 'created_at', type: 'timestamptz', nullable: true })
   createdAt: Date;
 
   @ManyToOne(() => ConversationEntity, (conversation) => conversation.messages)