save_progress() rewrites the whole file on every request

[CyberSunil]

Every chat turn, hint, and live message serialises all sessions and rewrites progress.json. Fine for one player, but the scoreboard is shared, so a classroom or workshop hitting one instance will feel it. Investigate batching writes or only persisting on state-changing events.

File: app.py

[aditi-2400]

Hi @CyberSunil , I'd like to work on this one. My plan is to add a dirty flag to track when session state actually changes, so save_progress() only writes when there's something new to persist, rather than rewriting the whole file on every chat turn or hint. Let me know if that approach sounds right or if you had something else in mind, and I'll get started.