- Add WeekStartDay and DefaultDueTime fields to Config struct
- Set defaults: week_start_day=monday, default_due_time=empty
- Add GetWeekStart() and GetDefaultDueTime() helper methods
- Update ParseDate() to use configured week start day
- All tests passing
- Create DateParser struct with configurable base time and week start
- Add placeholder methods for new parsing features
- Implement time-of-day parsing foundation (splitDateTime, parseTimeOfDay)
- Maintain backward compatibility with existing ParseDate() function
- Update tests to use new DateParser API
- All 33 existing tests passing