fix(diary): JournalResp 补充 assigned_topic_id 字段

- dto.rs: JournalResp 添加 assigned_topic_id: Option<Uuid>
- journal_service model_to_resp: 映射 model.assigned_topic_id
- parent_handler journal_model_to_resp: 同步映射

Flutter 端 JournalEntry 已有 assignedTopicId，无需修改
测试: 84/84 通过

crates/erp-diary/src/handler/parent_handler.rs

@@ -453,6 +453,7 @@ fn journal_model_to_resp(model: crate::entity::journal_entry::Model) -> JournalR
         tags,
         is_private: model.is_private,
         shared_to_class: model.shared_to_class,
+        assigned_topic_id: model.assigned_topic_id,
         version: model.version,
         created_at: model.created_at,
         updated_at: model.updated_at,