Oversized request body: 413 with a short warning instead of 500 and an ERROR traceback

Found on the live server (3 MB JSON to /api/auth/login answered 500). Django raises
RequestDataTooBig for bodies over DATA_UPLOAD_MAX_MEMORY_SIZE and would answer 400, but our DRF
exception handler turned every unknown exception into 500 + logger.exception, so each large request
also wrote a full ERROR traceback. Other SuspiciousOperation subclasses now get Django's 400 as well.

Tested: 2 tests (the 413 one fails without the change). Verified on the server after deploy.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

config/tests_request_size.py

@@ -0,0 +1,31 @@
+"""
+بدنه‌ی درخواستِ بزرگ ۵۰۰ و ERRORِ لاگ نمی‌دهد (config/exceptions.py). روی سرورِ زنده، JSONِ ۳ مگابایتی به
+/api/auth/login ۵۰۰ داده بود؛ ۲۰۰ کیلوبایت درست ۴۰۰ می‌داد.
+"""
+import json
+
+from django.core.cache import cache
+from django.test import TestCase, override_settings
+from rest_framework.test import APIClient
+
+
+@override_settings(DATA_UPLOAD_MAX_MEMORY_SIZE=2_621_440)
+class OversizedBodyTests(TestCase):
+    def setUp(self):
+        cache.clear()
+
+    def _post(self, path, size):
+        body = json.dumps({'phone': '09120000000', 'otp': '1' * size})
+        return APIClient().post(path, data=body, content_type='application/json')
+
+    def test_a_body_over_the_limit_is_413_with_a_persian_message(self):
+        for path in ('/api/auth/login', '/api/auth/otp/request'):
+            with self.assertNoLogs('config.exceptions', 'ERROR'):
+                response = self._post(path, 3_000_000)
+            self.assertEqual(response.status_code, 413, path)
+            self.assertIn('حجم', response.json()['detail'])
+
+    def test_a_large_but_allowed_body_still_gets_the_normal_validation_error(self):
+        response = self._post('/api/auth/login', 200_000)
+        self.assertEqual(response.status_code, 400)
+        self.assertIn('otp', response.json())