Replaced string-based X-axis with numeric timestamp axis:
- Custom ChartXTick component renders hour marks at -35° angle
- New day boundaries shown in bold (e.g., 'Apr 29')
- Hour marks shown as '9:00 AM', '10:00 AM' etc.
- Tooltip shows full date+time on hover
- Direction timeline uses formatted timestamps
- Bottom margin increased to accommodate angled labels