Handle btcpay "paid" invoice status for sponsorship donations

backend/src/api/donations.ts

@@ -50,7 +50,7 @@ class Donations {
     }
 
     const response = await this.getStatus(data.id);
-    if (response.status !== 'complete' && response.status !== 'confirmed') {
+    if (response.status !== 'complete' && response.status !== 'confirmed' && response.status !== 'paid') {
       return;
     }