refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

plugins/domain/message_gateway/message_gateway_test.go

@@ -0,0 +1,30 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package message_gateway_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/Rain-kl/Wavelet/pkg/testhelper"
+	"github.com/Rain-kl/Wavelet/plugins/domain/message_gateway"
+)
+
+func TestUpsertPairingCode_ReusesUnexpired(t *testing.T) {
+	_, _, cleanup := testhelper.SetupTestEnvironment(t)
+	defer cleanup()
+	ctx := context.Background()
+	first, err := message_gateway.UpsertPairingCode(ctx, 1, "tg-1", "ABCD1234", time.Now().Add(15*time.Minute))
+	if err != nil {
+		t.Fatal(err)
+	}
+	second, err := message_gateway.UpsertPairingCode(ctx, 1, "tg-1", "ZZZZ9999", time.Now().Add(15*time.Minute))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if first.Code != second.Code || first.Code != "ABCD1234" {
+		t.Fatalf("reuse failed: %+v %+v", first, second)
+	}
+}