新增首页 AW炫彩回收入口，支持后台配置展示图

首页第三入口点击查看回收说明图；配置项 mobile.aw_recycle 可配标题/图片；aw-recycle 走公开文件链路，首页鉴权预览兼容旧私有地址。

backend/internal/modules/systemconfig/aw_recycle.go

@@ -0,0 +1,43 @@
+package systemconfig
+
+import (
+	"encoding/json"
+	"strings"
+)
+
+const awRecycleConfigKey = "mobile.aw_recycle"
+
+func defaultAWRecycle() AWRecycleConfig {
+	return AWRecycleConfig{
+		Title:    "AW炫彩回收",
+		Subtitle: "点击查看回收说明",
+		ImageURL: "",
+		Enabled:  true,
+	}
+}
+
+func defaultAWRecycleConfigValue() string {
+	raw, err := json.Marshal(defaultAWRecycle())
+	if err != nil {
+		return `{"title":"AW炫彩回收","subtitle":"点击查看回收说明","image_url":"","enabled":true}`
+	}
+	return string(raw)
+}
+
+func normalizeAWRecycle(item AWRecycleConfig) AWRecycleConfig {
+	def := defaultAWRecycle()
+	title := strings.TrimSpace(item.Title)
+	if title == "" {
+		title = def.Title
+	}
+	subtitle := strings.TrimSpace(item.Subtitle)
+	if subtitle == "" {
+		subtitle = def.Subtitle
+	}
+	return AWRecycleConfig{
+		Title:    title,
+		Subtitle: subtitle,
+		ImageURL: strings.TrimSpace(item.ImageURL),
+		Enabled:  item.Enabled,
+	}
+}