- Create dateUtils.ts with helpers for UTC conversion and timezone display
- Add TimezoneSerializerMixin to include business_timezone in API responses
- Update GeneralSettings timezone dropdown with IANA identifiers
- Apply timezone mixin to Event, TimeBlock, and field mobile serializers
- Document timezone architecture in CLAUDE.md
All times stored in UTC, converted for display based on business timezone.
If business_timezone is null, uses user's local timezone.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>