refactor(router): split route registration into v1 package categorizations

- Created `internal/router/v1` subpackage
- Split routes into `admin.go`, `user.go`, `public.go`, and `custom.go`
- Cleaned up imports and helper registration functions from `router.go`
- Removed obsolete `internal/router/custom.go`

internal/router/middlewares.go

@@ -2,6 +2,7 @@
 // Copyright 2026 Arctel.net
 // SPDX-License-Identifier: Apache-2.0
 
+// Package router 提供 HTTP 路由注册与服务启动
 package router
 
 import (