feat(admin): add admin endpoint to list user devices with JPush registration IDs

- Add AdminDeviceTokenResponse DTO including push_token (RegistrationID) for push debugging
- Add DeviceTokenToAdminResponse and DeviceTokensToAdminResponse converters
- Inject PushService into AdminUserHandler for retrieving user devices
- Register GET /api/v1/admin/users/:id/devices route for querying target user's device tokens

internal/router/router.go

@@ -546,6 +546,7 @@ func (r *Router) setupRoutes() {
 					admin.GET("/users", r.AdminUserHandler.GetUserList)
 					admin.GET("/users/:id", r.AdminUserHandler.GetUserDetail)
 					admin.PUT("/users/:id/status", r.AdminUserHandler.UpdateUserStatus)
+					admin.GET("/users/:id/devices", r.AdminUserHandler.GetUserDevices)
 				}
 
 				// 帖子管理