fix: Hub 连接清理顺序修复、OAuth 类型常量提取、disassociate 逻辑优化

- Hub proxy/worker 连接关闭时先 unregister 再延迟 abort writer，确保缓冲消息排空
- 提取 OAUTH_AUTH_TYPES 常量，替代各处硬编码的 OAuth 类型列表
- auto-disassociate 跳过 OAuth Key，避免其动态 allowed_models 干扰判定
- 删除 Key 时传入 skip_disassociate=True，跳过不必要的解关联检查
- ModelMapper 缓存命中时将 ORM 实例脱离 Session，修复 DetachedInstanceError

aether-hub/src/proxy_conn.rs

@@ -79,11 +79,16 @@ pub async fn handle_proxy_connection(
         .await;
     });
 
-    // Wait for reader to end, then cleanup writer/ping and unregister from hub.
+    // Wait for reader to end, then cleanup.
     let _ = reader.await;
     ping_task.abort();
-    writer.abort();
     hub.unregister_proxy(conn_id, &node_id);
+    // conn still holds an Arc<ProxyConn> with a channel sender clone.
+    // Drop it so the writer can drain and exit.
+    drop(conn);
+    tokio::time::sleep(Duration::from_millis(100)).await;
+    writer.abort();
+    let _ = writer.await;
 }
 
 async fn run_proxy_reader(

aether-hub/src/worker_conn.rs

@@ -65,11 +65,17 @@ pub async fn handle_worker_connection(
         .await;
     });
 
-    // Wait for reader to end, then cleanup writer/ping and unregister from hub.
+    // Wait for reader to end, then cleanup.
     let _ = reader.await;
     ping_task.abort();
-    writer.abort();
+    // Unregister first so all channel senders are dropped (reader_tx dropped
+    // when reader completes, ping_tx dropped by abort, conn.tx dropped when
+    // the last Arc<WorkerConn> is removed from hub). This lets the writer
+    // drain buffered messages (e.g. GOAWAY) before we force-abort it.
     hub.unregister_worker(conn_id);
+    tokio::time::sleep(Duration::from_millis(100)).await;
+    writer.abort();
+    let _ = writer.await;
 }
 
 async fn run_worker_reader(