fix: handle None question_text in classified edit page

Co-Authored-By: Claude (claude-opus-4-5-thinking) <noreply@anthropic.com>

classifier_routes.py

@@ -198,7 +198,7 @@ def edit_classified_questions():
     questions = []
     for q in questions_from_db:
         q_dict = dict(q)
-        plain_text = q_dict['question_text'] # It's already plain text from OCR
+        plain_text = q_dict.get('question_text') or ''  # Handle None
         q_dict['question_text_plain'] = (plain_text[:100] + '...') if len(plain_text) > 100 else plain_text
         questions.append(q_dict)