加 /api/cart/* 接口；加购链路完全归 trading

trading 新增 4 条购物车接口（POST /api/cart/{add,status,clear,remove}），
全部 Bearer 鉴权、走 SiteInteractor（Playwright + storage_state）。同步把
SiteInteractor 从 gateway URL 解耦——lifespan 总是构造与启停，container
字段 worker_site → site，加 asyncio.Lock 让 HTTP 与 worker 共用同一把锁
（同账号串行硬约束）。clear/remove 用 UI 点击 button[aria-label="削除"]，
探针回报这是稳定 selector；真账号实测前先用此路径。

抽 ichiba 加购字段解析到 app/shared/purchase_contract.py（常量 +
inventory_flag_for + basket_domain_of + base_form_fields），原本 scraping
与 trading 重复实现同一段 __INITIAL_STATE__.purchase 解析。进一步发现
README 写的「purchase 块是两服务契约」实际未落地——trading 必须 Playwright
开页（httpx 被 TLS 指纹拦死），本地抽比再调 /api/item_detail 更快更新鲜。
删除 scraping 端 PurchaseInfo/PurchaseOption/PurchaseOptionValue 模型、
各站 _purchase_info 函数、tests/test_purchase.py。ItemDetailData 保留
purchase_condition / is_sold_out / purchase_unit / sku 等商品状态字段。
README「加购与下单」段重写。

328 测试全绿（含架构测试守住三方互不 import）。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/scraping/parsers/subsites/brandavenue.py

@@ -18,7 +18,6 @@ from app.shared.errors import ScrapeParseError
 from app.scraping.models.scrape import (
     Breadcrumb,
     ItemDetailData,
-    PurchaseInfo,
     ShopSummary,
     SkuAttribute,
     SkuAxis,
@@ -37,44 +36,6 @@ SHOP_NAME = "Rakuten Fashion"
 _COLOR_AXIS = "カラー"
 _SIZE_AXIS = "サイズ"
 
-# cart_info.cart_url_type → 加购端点。站点前端用同名映射表（resolveCartUrl）解析；
-# 若该字段本身已经是一个 URL，则直接使用。
-_CART_URL_BY_TYPE = {
-    "1": "https://ts.basket.step.rakuten.co.jp/rms/mall/bs/cartadd/set",
-    "2": "https://ts.sp.basket.step.rakuten.co.jp/rms/mall/bss/cartadd/set",
-    "3": "https://t2.basket.step.rakuten.co.jp/rms/mall/bs/cartadd/set",
-    "4": "https://t2.sp.basket.step.rakuten.co.jp/rms/mall/bss/cartadd/set",
-    "5": "https://basket.step.rakuten.co.jp/rms/mall/bs/cartadd/set",
-    "6": "https://sp.basket.step.rakuten.co.jp/rms/mall/bss/cartadd/set",
-}
-_DEFAULT_PURCHASE_EVENT = "ES01_003_001"
-
-
-def _resolve_cart_url(cart_url_type: str) -> str:
-    if cart_url_type.startswith("http"):
-        return cart_url_type
-    return _CART_URL_BY_TYPE.get(cart_url_type, "")
-
-
-def _purchase_info(product: dict) -> PurchaseInfo:
-    """加购字段与市场是同一套契约，差别只在端点由 cart_url_type 映射得到"""
-    cart_info = as_dict(as_dict(product.get("rms_info")).get("cart_info"))
-    if not cart_info:
-        return PurchaseInfo()
-    return PurchaseInfo(
-        cart_url=_resolve_cart_url(as_str(cart_info.get("cart_url_type"))),
-        form_fields={
-            "shop_bid": as_str(cart_info.get("shop_bid")),
-            "item_id": as_str(cart_info.get("item_id")),
-            "inventory_flag": as_str(cart_info.get("inventory_type")),
-            "__event": as_str(cart_info.get("event")) or _DEFAULT_PURCHASE_EVENT,
-            "encode": "utf8",
-        },
-        quantity_field="units",
-        variant_field="variant_id",
-    )
-
-
 def validate(html: str) -> str | None:
     if "window.__INITIAL_STATE__" in html:
         return None
@@ -206,5 +167,4 @@ def parse(page: SubsitePage) -> ItemDetailData:
         genre_id=as_str(rms.get("genre_id")),
         breadcrumbs=_breadcrumbs(product),
         sku=_sku(product, include_variants=page.include_sku_variants),
-        purchase=_purchase_info(product),
     )