refactor(auth): modularize auth plugin with physical subpackages and decoupled services

backend/plugins/domain/auth/model/do/cached_token.go

@@ -0,0 +1,12 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package do provides domain data objects for the auth plugin.
+package do
+
+// CachedToken represents the minimal cached representation of an access token.
+type CachedToken struct {
+	ID      uint64 `json:"id"`
+	UserID  uint64 `json:"user_id"`
+	IsAdmin bool   `json:"is_admin"`
+}