- Replace type assertions with type guards in types.ts (isDateString, isStringArray)
- Add useCallback for event handlers (handleTaskClick, handleKeyDown)
- Replace styled-jsx with CSS modules (gantt.module.css)
- Update tests to use CSS module class name patterns
- Add milestone support with diamond markers
- Implement dependency line rendering with SVG arrows
- Add isMilestone property to GanttTask type
- Create dependency calculation and visualization
- Add comprehensive tests for milestones and dependencies
- Add index module tests for exports
- Coverage: GanttChart 98.37%, types 91.66%, index 100%
