chore(openspec): archive add-shop-coupons

Sync the shop-coupons capability plus the order, frontend-mall, and
frontend-shop-admin requirements into the main specs, and write the capability
Purpose the archive leaves as a placeholder.

Renaming the coupon scenario in the flash-sales and group-buying order deltas
to the exact name now in the main order spec keeps those changes archivable,
since a MODIFIED requirement replaces the whole block.

openspec/specs/frontend-mall/spec.md

@@ -159,3 +159,18 @@ The buyer-center dashboard and points surfaces SHALL load the signed-in customer
 #### Scenario: account summary reload
 - **WHEN** a signed-in shopper reloads the buyer center
 - **THEN** displayed account statistics come from the selected API adapter and survive browser state loss
+
+### Requirement: Live shop coupon surfaces
+The mall SHALL load a product's currently claimable shop coupons and the signed-in customer's coupon list through the shared API client, replacing direct coupon fixtures. Checkout SHALL present eligible owned coupons separately for each shop order and show the server-returned discount after submission. Payment and order-detail views SHALL show the persisted `discount_minor` and post-discount total from the order payload.
+
+#### Scenario: claim from a product page
+- **WHEN** a signed-in shopper claims an active coupon with remaining stock from a product page
+- **THEN** it appears in the shopper's coupon list without a fixture import
+
+#### Scenario: select coupon by shop
+- **WHEN** a cart spans two shops and the shopper selects a coupon for one shop
+- **THEN** checkout submits the choice only for that shop and the other shop remains undiscounted
+
+#### Scenario: order shows realized discount
+- **WHEN** checkout succeeds with a coupon on one shop order
+- **THEN** that order's payment and detail views show the server discount and reduced total without a client-calculated amount