实现 site_interact 加购与购物车校验（Playwright 通道）

探针实测发现 httpx 因 TLS/HTTP2 指纹被 Rakuten 拒认（cookie 有效但
站点不识别 session），site_interact 改为全程 Playwright + storage_state。
add_to_cart 与 verify_cart 已实测可用：从商品页 __INITIAL_STATE__ 抽
purchase 块、调用方补 variant_id 与 choice、POST basketDomain、用 cart
count JSONP API 与 SPA 渲染后的 cart 页校验。enter_checkout 及之后仍
NotImplementedError：Rakuten 对 checkout 要求 session upgrade（重输密码），
是自动 checkout 的硬墙，未实测过墙方案前留接口缝。

SiteInteractor 类持有 Playwright BrowserContext，由 WorkerRunner 实例
持有、container/main 接线、lifespan 管理生命周期。测试侧 23 个用例，
全套件 333 passed，架构边界守住。

附 5 个探针脚本（scripts/probe_*.py），记录实测路径与响应结构。

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

app/trading/worker/runner.py

@@ -30,11 +30,12 @@ from typing import TYPE_CHECKING
 
 from app.shared.errors import AppError, OrderGuardError
 from app.shared.task_state import OrderState, TaskStatus
-from app.trading.worker import site_interact, verify
+from app.trading.worker import verify
 from app.trading.worker.client import GatewayClient
 from app.trading.worker.evidence import EvidenceStore
 from app.trading.worker.local_db import LocalDB
 from app.trading.worker.models import LeaseTask
+from app.trading.worker.site_interact import SiteInteractor
 
 if TYPE_CHECKING:
     from app.shared.config import Settings
@@ -67,11 +68,13 @@ class WorkerRunner:
         gateway_client: GatewayClient,
         local_db: LocalDB,
         evidence: EvidenceStore,
+        site: SiteInteractor,
     ):
         self._settings = settings
         self._gateway = gateway_client
         self._db = local_db
         self._evidence = evidence
+        self._site = site
         self._running = False
 
     def stop(self) -> None:
@@ -231,7 +234,7 @@ class WorkerRunner:
         # 步骤 1：加购
         await self._run_step(
             task, step_no=1, step_name="cart-add",
-            action=lambda: site_interact.add_to_cart(task),
+            action=lambda: self._site.add_to_cart(task),
             state=OrderState.IN_CART,
             detail="已加入购物车",
         )
@@ -239,14 +242,14 @@ class WorkerRunner:
         # 步骤 2：校验购物车
         await self._run_step(
             task, step_no=2, step_name="cart-check",
-            action=lambda: site_interact.verify_cart(task),
+            action=lambda: self._site.verify_cart(task),
             state=OrderState.IN_CART,
             detail="购物车已校验",
         )
 
         # 步骤 3：进入下单确认页 + 金额守卫
-        checkout_html = await site_interact.enter_checkout(task)
-        summary = await site_interact.parse_checkout(checkout_html)
+        checkout_html = await self._site.enter_checkout(task)
+        summary = await self._site.parse_checkout(checkout_html)
         self._enforce_amount_guard(task, summary.payable_yen)
         await self._run_step(
             task, step_no=3, step_name="order-confirm",
@@ -261,7 +264,7 @@ class WorkerRunner:
         )
 
         # 步骤 4：提交下单
-        site_order_id = await site_interact.submit_order(task)
+        site_order_id = await self._site.submit_order(task)
         await self._run_step(
             task, step_no=4, step_name="order-submit",
             action=self._noop(),
@@ -273,7 +276,7 @@ class WorkerRunner:
         # 步骤 5：付款
         await self._run_step(
             task, step_no=5, step_name="payment",
-            action=lambda: site_interact.pay(task, site_order_id),
+            action=lambda: self._site.pay(task, site_order_id),
             state=OrderState.AWAITING_PAYMENT,
             site_order_id=site_order_id,
             payable_yen=summary.payable_yen,
@@ -294,7 +297,7 @@ class WorkerRunner:
 
         # 步骤 6：付款后监控（非阻塞，常驻轮询；当前未实现）
         try:
-            await site_interact.monitor(task, site_order_id)
+            await self._site.monitor(task, site_order_id)
         except NotImplementedError:
             logger.info("付款后监控未实现，跳过：task_id=%s", task.task_id)