redraw the figure on follow-ups that only change the numbers; add a local fake OpenAI server

"What if 6 were 4?" has no shape word, so the diagram hint never went next to
it and the tutor would answer without a new figure. When the previous user
question in the conversation had one, a soft hint (redraw only if this
continues that problem) and the same catalog sections now go along.

tools/fake_openai.py stands in for GapGPT locally so the whole tutor path can be
exercised without credit: 12 scripted answers across grades 6-12 went through
streaming, block splitting, repair, storage, history and rendering in the real
chat screen.

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

.gitignore

@@ -20,3 +20,4 @@ staticfiles/
 
 # دیتابیسِ فایلیِ تست‌ها (config/settings.py → DATABASES.TEST)
 .test-db.sqlite3*
+tools/fake_openai_requests.jsonl