feat(marketing): 新增营销图管理模块

- 新增 marketing 模块：model/repository/service/handler 四层架构
- 数据模型：marketing_categories、marketing_templates、marketing_user_downloads
- 小程序端接口：分类列表、模板列表/详情、下载记录、广告回调
- 管理后台接口：分类/模板 CRUD、下载统计（X-Admin-Token 鉴权）
- 路由注册：接入现有 AuthMiddleware，新增 AdminTokenMiddleware
- Web 管理后台：单页面 Vue3 + Element Plus（分类管理、模板管理、数据概览）

Closes #37, #38, #39, #40

Made-with: Cursor

internal/routes/marketing_routes.go

@@ -0,0 +1,50 @@
+package routes
+
+import (
+	"github.com/gin-gonic/gin"
+
+	marketinghandler "wx_service/internal/marketing/handler"
+)
+
+func registerMarketingRoutes(
+	api *gin.RouterGroup,
+	protected *gin.RouterGroup,
+	adminToken string,
+	categoryHandler *marketinghandler.CategoryHandler,
+	templateHandler *marketinghandler.TemplateHandler,
+	downloadHandler *marketinghandler.DownloadHandler,
+) {
+	if categoryHandler == nil || templateHandler == nil || downloadHandler == nil {
+		return
+	}
+
+	marketing := api.Group("/marketing")
+	{
+		marketing.GET("/categories", categoryHandler.ListEnabled)
+		marketing.GET("/templates", templateHandler.ListEnabled)
+		marketing.GET("/templates/:id", templateHandler.GetDetail)
+	}
+
+	protectedMarketing := protected.Group("/marketing")
+	{
+		protectedMarketing.POST("/downloads", downloadHandler.Create)
+		protectedMarketing.POST("/ad_callback", downloadHandler.AdCallback)
+		protectedMarketing.GET("/downloads", downloadHandler.ListByUser)
+	}
+
+	admin := api.Group("/admin/marketing")
+	admin.Use(marketinghandler.AdminTokenMiddleware(adminToken))
+	{
+		admin.GET("/categories", categoryHandler.AdminList)
+		admin.POST("/categories", categoryHandler.AdminCreate)
+		admin.PUT("/categories/:id", categoryHandler.AdminUpdate)
+		admin.DELETE("/categories/:id", categoryHandler.AdminDelete)
+
+		admin.GET("/templates", templateHandler.AdminList)
+		admin.POST("/templates", templateHandler.AdminCreate)
+		admin.PUT("/templates/:id", templateHandler.AdminUpdate)
+		admin.DELETE("/templates/:id", templateHandler.AdminDelete)
+
+		admin.GET("/stats", downloadHandler.AdminStats)
+	}
+}