refactor(plugins): restructure admin and message_gateway into standard layered sub-packages

backend/plugins/domain/system/plugin.go

@@ -8,6 +8,7 @@ import (
 	"Wavelet/core"
 	"Wavelet/core/contracts"
 	"Wavelet/pkg/config"
+	"Wavelet/pkg/logger"
 	"Wavelet/pkg/response"
 	"net/http"
 	"reflect"
@@ -57,13 +58,9 @@ func (p *Plugin) Apply(ctx *core.Context) error {
 
 	// 2. Public config
 	ctx.Router().GET("/api/v1/config/public", func(c *gin.Context) {
-		type configItem struct {
-			Key   string `json:"key"`
-			Value string `json:"value"`
-		}
-		var configs []configItem
-		if dbSvc, err := core.Inject[contracts.DBService](ctx); err == nil && dbSvc != nil {
-			_ = dbSvc.DB(c.Request.Context()).Table("w_system_configs").Where("visibility = ?", "visible").Find(&configs).Error
+		configs, err := listPublicSystemConfigs(c.Request.Context(), ctx)
+		if err != nil {
+			logger.ErrorF(c.Request.Context(), "[System] query public system configs failed: %v", err)
 		}
 		c.JSON(http.StatusOK, response.OK(gin.H{
 			"configs": configs,

backend/plugins/domain/system/repository.go

@@ -0,0 +1,35 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package system
+
+import (
+	"Wavelet/core"
+	"Wavelet/core/contracts"
+	"context"
+)
+
+// publicSystemConfig 前端公共配置接口的只读投影。
+type publicSystemConfig struct {
+	Key   string `json:"key"`
+	Value string `json:"value"`
+}
+
+// listPublicSystemConfigs 读取对前端可见的系统配置项。
+//
+// 注意：w_system_configs 的所有者插件是 admin，contracts 目前尚未暴露读取契约，
+// 因此此处仍只能直连只读查询；待 admin 提供 SettingsService 契约后应改为调用契约。
+func listPublicSystemConfigs(ctx context.Context, appCtx *core.Context) ([]publicSystemConfig, error) {
+	dbSvc, err := core.Inject[contracts.DBService](appCtx)
+	if err != nil {
+		return nil, err
+	}
+	if dbSvc == nil {
+		return nil, nil
+	}
+	var configs []publicSystemConfig
+	err = dbSvc.DB(ctx).Table("w_system_configs").
+		Where("visibility = ?", "visible").
+		Find(&configs).Error
+	return configs, err
+}