[P2] Event analytics and insights

[KalebCole]

Priority: P2 (Medium) Analytics and insights across your events. ## Proposed Commands bash # Stats for single event partiful stats <eventId> # Overall hosting stats partiful stats --all # Attendance trends partiful stats --trend ## Output Your Partiful Stats (Last 12 months) ==================================== Events hosted: 24 Total guests: 312 unique people Average attendance: 13 per event Most popular day: Saturday Best performing: "Game Night" series (avg 18 attendees) Top attendees: 1. John Doe - 18 events 2. Jane Smith - 15 events 3. Bob Wilson - 12 events ## Acceptance Criteria - [ ] Per-event stats (invited/going/showed) - [ ] Aggregate stats across events - [ ] Attendance trends over time - [ ] Top attendees ranking