refactor(message): simplify state management and remove redundant service methods

Refactor the message module to streamline state management by removing the `MessageStateManager` and `SubscriptionManager` layers, relying instead on Zustand's built-in selector mechanism for reactive updates.

- Remove redundant `setConversations`, `addMessage`, and `updateMessage` actions from the Zustand store to favor more specialized update methods.
- Clean up `MessageService` by removing deprecated conversation and message sending convenience methods.
- Update service interfaces to support new synchronization capabilities including `syncBySeq` and `restartSources`.
- Simplify documentation and comments across the message store and its associated services.

src/stores/message/services/MessageSyncService.ts

@@ -1,10 +1,6 @@
 /**
  * 消息同步服务
  * 处理消息和会话的服务器同步逻辑
- * 
- * 重构说明：
- * - 直接使用 zustand store 替代 IMessageStateManager
- * - 移除了 SubscriptionManager 调用，Zustand 的 set() 会自动触发组件重渲染
  */
 
 import type { ConversationResponse, MessageResponse } from '../../../types/dto';