refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

pkg/task/constants.go

@@ -0,0 +1,14 @@
+// Copyright 2025 linux.do
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package task 定义异步任务类型与调度常量
+package task
+
+// 任务队列名称
+const (
+	QueueDefault = "default"
+)
+
+// DefaultMaxRetry 任务默认最大重试次数
+const DefaultMaxRetry = 3