Change default SCRAPER_TIMEZONE from UTC to America/Denver so that
scrape date records (date_checked, daily summaries) reflect local time.
A late-night manual scrape and early-morning automated scrape will no
longer both report as the same UTC day.
Updated getTodayUTC/getTodayDateUTC helpers to use toLocaleDateString
with the configured timezone. ISO timestamps for last_scraped, first_seen,
startedAt etc. remain in UTC as they represent precise moments.
