Date-only strings parsed with new Date(dateStr + 'T00:00:00') were
interpreted relative to the local timezone, causing off-by-one day
display for users west of UTC. Fixed across 16 files by parsing as
UTC ('T00:00:00Z') and displaying with timeZone: 'UTC'.
Users can now select which days are weekends (default: Sat+Sun).
Useful for countries like Bangladesh (Fri+Sat) or others with
different work weeks. Settings appear under "Block weekends" toggle.