feat(server): outbox relay 改为 LISTEN/NOTIFY + 30s 兜底轮询

- EventBus::publish() 持久化后执行 NOTIFY outbox_channel
- outbox relay 使用 sqlx::PgListener 监听 + tokio::select! 竞争
- 30s 兜底轮询防止 NOTIFY 丢失，断线自动重连
- 轮询间隔从 5s 提升到 30s，事件延迟降至 <100ms

crates/erp-server/Cargo.toml

@@ -17,6 +17,7 @@ tracing.workspace = true
 tracing-subscriber.workspace = true
 config.workspace = true
 sea-orm.workspace = true
+sqlx.workspace = true
 redis.workspace = true
 utoipa.workspace = true
 serde_json.workspace = true