feat(mall): claim and redeem shop coupons from the storefront

The product page loads a shop's claimable coupons through the shared client and
claims them in place; the buyer coupon list reads owned snapshots with their
claimed/redeemed/expired state. Checkout offers each shop order at most one
owned coupon and submits only the choice; the pay page and order detail render
the server-persisted discount and reduced total, never a client figure.

Coupon fixtures leave the pages; the fixed-data adapter still serves the coupon
domain as the rollback path. The demo seed creates two deterministic templates
and claims them for the demo customer.

apps/mall/locales/checkout.ts

@@ -23,6 +23,9 @@ export default {
       alipay: "Alipay",
       payTitle: "Pay for your order",
       orderNo: "Order no.",
+      coupon: "Coupon",
+      noCoupon: "No coupon",
+      couponDiscount: "Coupon discount",
       grandTotal: "Total payment",
       confirmPay: "Confirm payment",
       noPendingOrders: "There are no orders waiting for payment.",
@@ -58,6 +61,9 @@ export default {
       alipay: "支付宝",
       payTitle: "订单支付",
       orderNo: "订单号",
+      coupon: "优惠券",
+      noCoupon: "不使用优惠券",
+      couponDiscount: "优惠券抵扣",
       grandTotal: "应付总额",
       confirmPay: "确认支付",
       noPendingOrders: "暂无待支付订单。",

apps/mall/locales/product.ts

@@ -13,6 +13,9 @@ export default {
       coupon: "Coupon",
       coupons: "Available coupons",
       claim: "Claim",
+      claimed: "Claimed",
+      claimFailed: "Unable to claim this coupon",
+      loginToClaim: "Sign in to claim",
       choose: "Choose",
       selected: "Selected",
       quantity: "Quantity",
@@ -58,6 +61,9 @@ export default {
       coupon: "优惠券",
       coupons: "可用优惠券",
       claim: "领取",
+      claimed: "已领取",
+      claimFailed: "优惠券领取失败",
+      loginToClaim: "登录后领取",
       choose: "选择",
       selected: "已选",
       quantity: "数量",

apps/mall/locales/user.ts

@@ -83,6 +83,10 @@ export default {
       threshold: "Minimum spend",
       expiresAt: "Expires",
       noCoupons: "No coupons yet.",
+      couponStatus: "Status",
+      couponClaimed: "Claimed",
+      couponRedeemed: "Used",
+      couponExpired: "Expired",
       invoicesTitle: "My invoices",
       invoiceNo: "Invoice no.",
       invoiceOrderNo: "Order no.",
@@ -176,6 +180,10 @@ export default {
       threshold: "使用门槛",
       expiresAt: "有效期至",
       noCoupons: "暂无优惠券。",
+      couponStatus: "状态",
+      couponClaimed: "未使用",
+      couponRedeemed: "已使用",
+      couponExpired: "已过期",
       invoicesTitle: "我的发票",
       invoiceNo: "发票号",
       invoiceOrderNo: "订单号",