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/file/storage_test.go

@@ -29,3 +29,14 @@ func TestNormalizeSceneAllowsAnnouncement(t *testing.T) {
 		t.Fatalf("normalize announcement scene = %q", got)
 	}
 }
+
+func TestAWRecycleSceneUsesPublicFileURL(t *testing.T) {
+	if got := normalizeScene("aw-recycle"); got != "aw-recycle" {
+		t.Fatalf("normalize aw-recycle scene = %q", got)
+	}
+	key := "aw-recycle/2026/07/19/example.webp"
+	got := fileURLForScene("aw-recycle", key)
+	if !strings.HasPrefix(got, "/api/public/files/object?") {
+		t.Fatalf("aw-recycle file url = %q, want public file endpoint", got)
+	}
+}