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-shop-admin/spec.md

@@ -2,7 +2,9 @@
 
 ## Purpose
 The merchant console for managing a shop's products and fulfilling its orders.
+
 ## Requirements
+
 ### Requirement: Merchant product management
 Shop users SHALL manage only their own shop's products: create/edit bilingual content, manage SKUs, publish/unpublish with immediate effect on the storefront.
 
@@ -17,3 +19,13 @@ Shop users SHALL see incoming orders, create shipments, mark them shipped, and i
 - **WHEN** a merchant creates a shipment for a paid order and marks it shipped
 - **THEN** the shopper sees the shipment with tracking info
 
+### Requirement: Merchant coupon management
+Shop users SHALL manage only their shop's coupon templates from shop-admin, including localized title, amount and threshold in minor units, currency, claim stock, active window, and enabled state. Shop-admin SHALL expose a coupons navigation entry beside existing shop operations.
+
+#### Scenario: create an active template
+- **WHEN** a shop owner creates a valid coupon template
+- **THEN** the template is available for eligible customers to claim during its active window
+
+#### Scenario: coupons appear in shop navigation
+- **WHEN** an authenticated shop user opens shop-admin
+- **THEN** a coupons management entry is reachable without leaving the shop-scoped console