feat: add event type filter to analytics activity stream

[aalvaropc]

Summary

• Dropdown filter in the Recent Activity section of the analytics page
• Populated dynamically from distinct event types in the workspace
• Filters activity stream in real-time on selection change
• Preserves filter when switching time range (7d/30d/90d)
• Uses existing Audit.list_events/2 :event_type option and Audit.distinct_event_types/1

Test plan

• mix precommit — 638 tests, 0 failures
• Manual: navigate to Analytics, select an event type from dropdown, verify stream filters