feat(message-gateway): add admin channel CRUD APIs

internal/apps/admin/message_gateway/errs.go

@@ -0,0 +1,14 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package message_gateway
+
+const (
+	errNameRequired          = "name is required"
+	errTypeInvalid           = "type must be telegram or qq"
+	errTelegramTokenRequired = "bot_token is required"
+	errQQCredentialsRequired = "app_id and app_secret are required"
+	errChannelNotFound       = "channel not found"
+	errChannelProbeFailed    = "channel probe failed"
+	maskedSecret             = "********"
+)