Events scheduled for today were appearing in tomorrow's column due to
raw millisecond arithmetic not handling timezone transitions properly.
Changes:
- Replace MILLISECONDS_IN_DAY * day arithmetic with Date.setDate()
- Fix mutation bug where date parameter was being modified
- Use proper calendar day arithmetic that handles DST/timezone
Tested in Brisbane timezone (GMT+10) - events now display in correct column.
Signed-off-by: Dominic O'Carroll <99632940+domocarroll@users.noreply.github.com>
Co-authored-by: Dom Carroll <dom@subfrac.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>