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>

rag/tests.py

@@ -104,7 +104,7 @@ class AskAIRagPathTests(TestCase):
              patch('rag.services.clients.get_qdrant_client', return_value=_FakeQdrant()):
             resp = self._ask({'userQuestion': 'یک سوالِ کلی'})
         self.assertEqual(resp.status_code, 200, resp.content)
-        self.assertEqual(resp.data['answer'], 'پاسخِ عمومی.')
+        self.assertEqual(resp.data['answer'], 'پاسخ عمومی.')
         self.assertEqual(resp.data['usedChunks'], [])
 
     def test_provider_failure_becomes_503_and_releases_slot(self):