fix: correct WORKERS var, export path, and seamless marquee loop

- entrypoint.sh: use GUNICORN_WORKERS to match example.env (#17)
- guestbook_export.py: read DATABASE_PATH from env instead of
  hardcoded relative path (#18)
- Scrolling marquee: duplicate guest list for seamless loop,
  animate translateX(0) to translateX(-50%), increase font to
  1.25rem, fix JS speed calc to use half content width (#20)

entrypoint.sh

@@ -4,5 +4,4 @@
 envsubst < /app/templates/index.html.template > /app/templates/index.html
 
 # Start Gunicorn; using an environment variable for workers (default is 3)
-# TODO: Variable mismatch — example.env sets GUNICORN_WORKERS but this reads WORKERS. Change to ${GUNICORN_WORKERS:-3}.
-exec gunicorn --bind 0.0.0.0:8000 app:app --workers ${WORKERS:-3}
+exec gunicorn --bind 0.0.0.0:8000 app:app --workers ${GUNICORN_WORKERS:-3}