Add fat_zebra payment processor

ENG-4633

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: horgh

HISTORY.rst

@@ -10,8 +10,8 @@ History
   token generated by the `Device Tracking Add-on
   <https://dev.maxmind.com/minfraud/track-devices>`_ for explicit device
   linking.
-* Added ``banquest``, ``summit_payments``, and ``yaadpay`` to the
-  ``/payment/processor`` validation.
+* Added ``banquest``, ``fat_zebra``, ``summit_payments``, and ``yaadpay`` to
+  the ``/payment/processor`` validation.
 * The version is now retrieved from package metadata at runtime using
   ``importlib.metadata``. This reduces the chance of version inconsistencies
   during releases.

src/minfraud/validation.py

@@ -175,6 +175,7 @@ def _hostname(hostname: str) -> str:
         "epx",
         "eway",
         "exact",
+        "fat_zebra",
         "first_atlantic_commerce",
         "first_data",
         "fiserv",