refactor(msg_gateway): decouple bot gateway and push notification architecture

- Split shared monolithic consts into bot, push, and errs with typed sentinel errors
- Restructure model layer into distinct bot and push subdomains
- Refactor DAO layer to enforce single-owner principle and remove cross-table raw SQL queries
- Decompose 1150+ line service/push.go into push_channel, push_event, push_trigger, push_worker, and push_template
- Clean up controller layer with generic request handlers and parameter validation in controller/base.go
- Streamline plugin.go to core Cordis lifecycle orchestration and remove re-export bloat
- Verify all unit tests, race tests, Cordis architecture rules, and Swagger generation pass cleanly

backend/plugins/domain/msg_gateway/service/bot_pairing_test.go

@@ -0,0 +1,27 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package service_test
+
+import (
+	"Wavelet/plugins/domain/msg_gateway/consts"
+	"Wavelet/plugins/domain/msg_gateway/service"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenerateCode_AlphabetAndLength(t *testing.T) {
+	code, err := service.GenerateCode()
+	require.NoError(t, err)
+	assert.Len(t, code, consts.CodeLength)
+	for _, r := range code {
+		assert.Contains(t, consts.CodeAlphabet, string(r))
+	}
+}
+
+func TestNormalizeAndFormat(t *testing.T) {
+	assert.Equal(t, "ABCDEFGH", service.NormalizeCode("ab-cd-ef-gh"))
+	assert.Equal(t, "ABCD-EFGH", service.FormatCode("ABCDEFGH"))
+}