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)

scripts/guestbook_export.py

@@ -1,9 +1,8 @@
 import csv
+import os
 import sqlite3
 
-# TODO: Hardcoded relative path — breaks if script is run from a different directory.
-# Replace with: DATABASE = os.environ.get('DATABASE_PATH', 'guestbook.db') and import os.
-DATABASE = 'guestbook.db'
+DATABASE = os.environ.get('DATABASE_PATH', 'guestbook.db')
 EXPORT_FILE = 'mailchimp_export.csv'
 
 def export_guestbook_to_csv():