har_audit: fix messaging endpoint URL fragment (fresa → dml/graphql.json)

Booking.com messaging ops (conversationMessages, postFreeTextMessage) moved
to dml/graphql.json; the old fresa/extranet/messaging/graphql path no longer
receives these calls. The client already uses the correct endpoint — this
aligns the audit manifest so HAR checks can find them.

scripts/har_audit.py

@@ -87,7 +87,7 @@ _BOOKING_ENDPOINTS: dict[str, dict] = {
     },
   },
   'conversationMessages': {
-    'url_fragment': 'fresa/extranet/messaging/graphql',
+    'url_fragment': 'dml/graphql.json',
     'operation_name': 'conversationMessages',
     'hint': 'open any guest message thread',
     'headers': {
@@ -95,7 +95,7 @@ _BOOKING_ENDPOINTS: dict[str, dict] = {
     },
   },
   'postFreeTextMessage': {
-    'url_fragment': 'fresa/extranet/messaging/graphql',
+    'url_fragment': 'dml/graphql.json',
     'operation_name': 'postFreeTextMessage',
     'hint': 'send a message to a guest',
     'headers': {