fix(dlc): 更新暗影哥特、黑色上衣与浪漫天命的商品编码

- 同步上游 DLC (聚鑫源) 最新 GoodID 映射：
  - suit_shadow_gothic: 6a13aa55e3bce430aca29b01
  - top_black_elite_trainer: 6a13aaeae3bce430aca29b03
  - suit_romantic_destiny: 6a13ab21e3bce430aca29b04
- 更新 delivery_helpers 缺省兜底映射表与 sync_product_images 常量
- 更新 provider_test 单元测试断言与 docs/商品目录.md 文档
- 验证方式：go test 单元测试通过，go vet 校验通过

backend/internal/service/delivery_helpers.go

@@ -82,14 +82,14 @@ func deliveryGoodID(channel, sku string) string {
 	}
 	return map[string]string{
 		"suit_alan_walker":        "682ef3c5a8f40c4234c59f47",
-		"suit_shadow_gothic":      "682ef39ca8f40c4234c59f36",
-		"top_black_elite_trainer": "682ef39ca8f40c4234c59f37",
+		"suit_shadow_gothic":      "6a13aa55e3bce430aca29b01",
+		"top_black_elite_trainer": "6a13aaeae3bce430aca29b03",
 		"m416_hamster_gray":       "682ef3c5a8f40c4234c59f52",
 		"bag_cute_bear":           "682ef3c5a8f40c4234c59f4a",
 		"suit_dual_fluffy":        "682ef3c5a8f40c4234c59f49",
 		"suit_pink_sheep":         "682ef3c5a8f40c4234c59f4d",
 		"suit_first_peach":        "682ef3c5a8f40c4234c59f48",
-		"suit_romantic_destiny":   "682ef39ca8f40c4234c59f38",
+		"suit_romantic_destiny":   "6a13ab21e3bce430aca29b04",
 		"pack_western_cowboy":     "682ef3c5a8f40c4234c59f4c",
 		"smoke_pink_sheep":        "682ef3c5a8f40c4234c59f50",
 		"frag_pink_sheep":         "682ef3c5a8f40c4234c59f51",

backend/internal/service/provider_test.go

@@ -52,7 +52,7 @@ func TestParseProductRoutingConfig(t *testing.T) {
 	if cfg5.RoutingMode != RoutingModePriority {
 		t.Fatalf("expected priority for dual-capable legacy config, got %s", cfg5.RoutingMode)
 	}
-	if cfg5.DLCGoodID != "682ef39ca8f40c4234c59f38" {
+	if cfg5.DLCGoodID != "6a13ab21e3bce430aca29b04" {
 		t.Fatalf("expected builtin DLC good id, got %s", cfg5.DLCGoodID)
 	}