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_runner_test.go

@@ -0,0 +1,34 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package service_test
+
+import (
+	"Wavelet/plugins/domain/msg_gateway/model/do"
+	"Wavelet/plugins/domain/msg_gateway/service"
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type stubChannel struct{}
+
+func (stubChannel) Type() string                                                 { return "stub" }
+func (stubChannel) Connect(context.Context) error                                { return nil }
+func (stubChannel) Disconnect(context.Context) error                             { return nil }
+func (stubChannel) Send(context.Context, do.Recipient, do.OutboundMessage) error { return nil }
+func (stubChannel) Capabilities() do.Capability                                  { return do.Capability{Text: true} }
+
+func TestRegisterLookup(t *testing.T) {
+	service.Register("stub", func(do.ChannelConfig, service.Handler) (service.Channel, error) {
+		return stubChannel{}, nil
+	})
+	fn, ok := service.Lookup("stub")
+	require.True(t, ok)
+
+	ch, err := fn(do.ChannelConfig{}, nil)
+	require.NoError(t, err)
+	assert.Equal(t, "stub", ch.Type())
+}