feat(core): EventBus dead-letter + consume_with_retry 辅助函数

- 新增 dead_letter_events 表 + Entity
- consume_with_retry: 幂等检查 + 成功标记 + 失败转入 dead-letter
- insert_dead_letter: 写入失败事件供后续排查和手动重试

crates/erp-core/src/entity/dead_letter_event.rs

@@ -0,0 +1,27 @@
+use sea_orm::entity::prelude::*;
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, PartialEq, DeriveEntityModel, Serialize, Deserialize)]
+#[sea_orm(table_name = "dead_letter_events")]
+pub struct Model {
+    #[sea_orm(primary_key, auto_increment = false)]
+    pub id: Uuid,
+    #[sea_orm(skip_serializing_if = "Option::is_none")]
+    pub tenant_id: Option<Uuid>,
+    pub original_event_id: Uuid,
+    pub event_type: String,
+    #[sea_orm(skip_serializing_if = "Option::is_none")]
+    pub payload: Option<serde_json::Value>,
+    pub consumer_id: String,
+    pub attempts: i32,
+    #[sea_orm(skip_serializing_if = "Option::is_none")]
+    pub last_error: Option<String>,
+    pub created_at: DateTimeUtc,
+    #[sea_orm(skip_serializing_if = "Option::is_none")]
+    pub resolved_at: Option<DateTimeUtc>,
+}
+
+#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
+pub enum Relation {}
+
+impl ActiveModelBehavior for ActiveModel {}

crates/erp-core/src/entity/mod.rs

@@ -1,3 +1,4 @@
 pub mod audit_log;
+pub mod dead_letter_event;
 pub mod domain_event;
 pub mod processed_event;