fix(input_sanitizer): add 'review_date' to default merchant sort fields

Add 'review_date' to support sorting merchant reviews when defaults are used

app/utils/input_sanitizer.py

@@ -243,9 +243,9 @@ class InputSanitizer:
         Allows endpoints to specify their own valid sort fields/orders while
         preserving sensible defaults for merchant search.
         """
-        # Defaults for merchant search endpoints
+        # Defaults for merchant search endpoints (include 'review_date' to support reviews when defaults are used)
         if valid_sort_fields is None:
-            valid_sort_fields = ['rating', 'price', 'distance', 'recommended', 'popularity', 'recent']
+            valid_sort_fields = ['rating', 'price', 'distance', 'recommended', 'popularity', 'recent', 'review_date']
         if valid_sort_orders is None:
             valid_sort_orders = ['asc', 'desc']