Allow users to customize when they receive notification reminders:
- Add hour fields to NotificationPreference model
- Add timezone conversion utilities (localHourToUtc, utcHourToLocal)
- Add time picker UI for iOS (wheel picker in sheet)
- Add time picker UI for Android (hour chip selector dialog)
- Times stored in UTC, displayed in user's local timezone
- Add localized strings for time picker UI
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
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