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

pkg/testhelper/gin.go

@@ -0,0 +1,20 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package testhelper
+
+import (
+	"github.com/Rain-kl/Wavelet/pkg/response"
+	"github.com/gin-gonic/gin"
+)
+
+// NewTestGinEngine 创建带 ErrorHandlerMiddleware 的 Gin 引擎，与生产环境错误响应行为一致。
+func NewTestGinEngine(middlewares ...gin.HandlerFunc) *gin.Engine {
+	gin.SetMode(gin.TestMode)
+	r := gin.New()
+	r.Use(response.ErrorHandlerMiddleware())
+	for _, middleware := range middlewares {
+		r.Use(middleware)
+	}
+	return r
+}