Features: - CRUD für Notizen, Anrufe, Emails, Meetings, Tasks - Timeline View für Kontakte/Firmen/Deals - Upcoming Tasks (nächste X Tage) - Overdue Tasks - Mark Complete/Reopen - Activity Statistics (by type, today, overdue) - Erinnerungen (reminder_at) - Duration Tracking - Outcome Recording Task: #11 Aktivitäten & Timeline