feat(email-tracking): add event timeline UI and analytics dashboard

[dviejokfs]

Summary

• Add GET /emails/events backend endpoint for listing tracking events across all emails with optional email_id and event_type filters
• Add EmailEventTimeline component to the email detail page — shows individual open/click/bounce/delivery events with IP, user-agent, clicked URLs, and bounce metadata
• Add EmailAnalytics tab to the Email settings page — rate cards (delivered, opened, clicked, bounced, complained with percentage bars) and a paginated global event log table

Test plan

• Navigate to Settings > Email > Analytics tab — verify rate cards and event log load
• Send a test email with track_opens: true and track_clicks: true
• Open the email (trigger pixel) and click a link — verify events appear in the timeline on the email detail page
• Filter events by type in both the detail timeline and the analytics tab
• Verify pagination works when there are >20 events
• Test mobile responsiveness — columns hide appropriately on smaller screens