Replace the AUTO/MONDAY/SUNDAY week-start enum with a sealed type (Auto + Day(DayOfWeek)) so users can pick any of the seven days as the first day of the week. The picker now lists "Automatic" plus all seven localised weekday names; labels come from java.time display names rather than per-day string resources. Stored values round-trip by DayOfWeek.name, so the legacy MONDAY/SUNDAY preferences migrate transparently. Garbage values fall back to Auto. Closes #3 (Codeberg) Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>