Add ZarinPal e-payment and related checkout/search fixes.

Business settings can store ZarinPal merchant credentials, and the payment registry can initiate and verify ZarinPal alongside Mellat.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/website-api/Meshkee-Website-API.postman_collection.json

@@ -1716,6 +1716,29 @@
             "url": "{{baseUrl}}/businesses/{{businessId}}/payments/mellat/callback",
             "description": "Called by Mellat (not by the website). Verifies+settles, then 303 redirect to returnUrl."
           }
+        },
+        {
+          "name": "ZarinPal callback (gateway → API)",
+          "request": {
+            "method": "GET",
+            "header": [],
+            "url": {
+              "raw": "{{baseUrl}}/businesses/{{businessId}}/payments/zarinpal/callback?Authority={{authority}}&Status=OK",
+              "host": ["{{baseUrl}}"],
+              "path": [
+                "businesses",
+                "{{businessId}}",
+                "payments",
+                "zarinpal",
+                "callback"
+              ],
+              "query": [
+                { "key": "Authority", "value": "{{authority}}" },
+                { "key": "Status", "value": "OK" }
+              ]
+            },
+            "description": "Called by ZarinPal (not by the website). Verifies payment, then 303 redirect to returnUrl."
+          }
         }
       ]
     },