feat(web): calendar import preview, repeat timer, CSV export, compact mode
- Calendar import preview: parse .ics → show events with conflict indicators → confirm/cancel before importing
- History page: repeat timer button (recreates alarm at same time-of-day, countdown with same duration)
- History page: CSV export (Label, Type, State, Urgency, Category, Created, Completed, Duration)
- Settings: compact mode toggle (persisted to localStorage, sets data-compact attribute)
- Updated roadmap Week 5 items
- 373 tests across 16 files, tsc clean