Refactor logging and drop deprecated FLASK_ENV

Move logging setup into max/log.py. The file handler is only used outside
debug mode and its directory is configurable via LOG_DIR. FLASK_ENV is
deprecated in Flask; debug mode is now controlled via FLASK_DEBUG.

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

Dockerfile

@@ -12,7 +12,6 @@ RUN mkdir log
 
 ENV PYTHONPATH=/app/
 ENV FLASK_APP=max.app
-ENV FLASK_ENV=production
 
 COPY max/ ./max
 COPY scripts/entrypoint.sh .