API output without Persian diacritics or written ezafe ی (company decision); tutor answers too

plain_persian() strips kasra/fatha/damma/shadda/sukun/hamza-above and the written «ه‌ی» ezafe, keeping tanwin. Applied
at output, not in data: PlainPersianJSONRenderer runs one byte-level pass over every JSON response (~5 ms per MB
locally), and to_plain() cleans tutor answers including the stream. Rewriting titles in the DB/seed would have broken
question binding by title path and SeedRecord keys. Tests updated to expect the cleaned text; config/tests_plain_persian.py.

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

ai_tutor/tests.py

@@ -65,7 +65,7 @@ class AskIdempotencyFollowUpsTests(TestCase):
 
         self.assertEqual(retry_response.status_code, 200)
         self.assertEqual(retry_response.data['suggestedFollowUps'], original_follow_ups)
-        self.assertEqual(retry_response.data['answer'], first_response.data['answer'])
+        self.assertEqual(retry_response.json()['answer'], first_response.json()['answer'])
         self.assertEqual(retry_response.data['messageId'], first_response.data['messageId'])
 
 
@@ -225,7 +225,7 @@ class AskAIConcurrentIdempotencyKeyTests(TestCase):
         # هر دو پاسخ باید دقیقاً به همون AskIdempotency (نتیجه‌ی برنده)
         # اشاره کنن.
         self.assertEqual(outer_response.data['messageId'], inner_response.data['messageId'])
-        self.assertEqual(outer_response.data['answer'], inner_response.data['answer'])
+        self.assertEqual(outer_response.json()['answer'], inner_response.json()['answer'])
 
         # فقط یک رکوردِ AskIdempotency برای این کلید باید وجود داشته باشه.
         self.assertEqual(