Remove useNostrOrders composable and related Checkout page

- Delete the useNostrOrders composable as it is no longer needed.
- Update MerchantStore.vue to utilize nostrmarketService for publishing orders instead of the removed composable.
- Refactor market store to check the readiness of nostrmarketService instead of useNostrOrders.
- Remove the Checkout.vue page, streamlining the checkout process and improving code maintainability.

src/modules/market/components/MerchantStore.vue

@@ -320,12 +320,11 @@ import {
   BarChart3
 } from 'lucide-vue-next'
 import type { OrderStatus } from '@/stores/market'
-import { nostrOrders } from '@/composables/useNostrOrders'
+import { nostrmarketService } from '../services/nostrmarketService'
 import { auth } from '@/composables/useAuth'
 
 const router = useRouter()
 const marketStore = useMarketStore()
-const nostrOrdersComposable = nostrOrders
 
 // Local state
 const isGeneratingInvoice = ref<string | null>(null)
@@ -502,7 +501,7 @@ const sendInvoiceToCustomer = async (order: any, invoice: any) => {
 
     // Send the updated order to the customer via Nostr
     // This will include the invoice information
-    await nostrOrdersComposable.publishOrderEvent(updatedOrder, order.buyerPubkey)
+    await nostrmarketService.publishOrder(updatedOrder, order.buyerPubkey)
     
     console.log('Updated order with invoice sent via Nostr to customer:', order.buyerPubkey)
   } catch (error) {