🔒️(backend) disable BrowsableAPIRenderer to prevent information leakage

Remove BrowsableAPIRenderer from API options, restricting output to JSON
format only. Prevents leakage of sensitive information like resource IDs and
user identifiers that were previously exposed in renderer dropdown options.

Issue identified in #YWH-PGM14336-4 report.
These information was considered as a critical disclosure by hackers.

src/backend/meet/settings.py

@@ -263,6 +263,9 @@ class Base(Configuration):
             "rest_framework.parsers.JSONParser",
             "nested_multipart_parser.drf.DrfNestedParser",
         ],
+        "DEFAULT_RENDERER_CLASSES": [
+            "rest_framework.renderers.JSONRenderer",
+        ],
         "EXCEPTION_HANDLER": "core.api.exception_handler",
         "DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.PageNumberPagination",
         "PAGE_SIZE": 20,