Add NostrmarketAPI integration and enhance MerchantStore component

- Introduce NostrmarketAPI service for improved merchant profile management.
- Update MerchantStore component to handle loading and error states during merchant profile checks.
- Implement logic to check for merchant profiles using the new API, enhancing user experience.
- Refactor computed properties and lifecycle methods to accommodate the new API integration.

These changes streamline the process of checking and managing merchant profiles, providing users with real-time feedback and improving overall functionality.

src/app.config.ts

@@ -36,7 +36,10 @@ export const appConfig: AppConfig = {
       config: {
         defaultCurrency: 'sats',
         paymentTimeout: 300000, // 5 minutes
-        maxOrderHistory: 50
+        maxOrderHistory: 50,
+        apiConfig: {
+          baseUrl: import.meta.env.VITE_LNBITS_BASE_URL || 'http://localhost:5000'
+        }
       }
     },
     chat: {