Add Event Archivation Functionality

[ivanskv2000]

Goal:
Introduce soft archiving for events — to allow hiding outdated or deprecated events without deleting them permanently.

Behavior

• Each event has an is_archived: boolean flag
• Archived events:
  • Are excluded by default from all API endpoints (unless explicitly requested)
  • Can be restored (unarchived) later
  • Are displayed in a visually distinct way in the UI
  • Cannot be edited unless unarchived

Backend Tasks

• Add is_archived field (default false) to Event model
• Update all event-related endpoints to exclude archived events by default:
  • GET /events
  • Forbid updating archived events on PUT /events
  • Forbid adding an archived event on POST /events
• Add query parameter include_archived=true to GET /events
• Add endpoint(s) for:
  • POST /events/{id}/archive
  • POST /events/{id}/unarchive

Frontend Tasks

• Add “Archive” button in event detail view (same style as Delete, with confirmation modal)
• Add “Unarchive” button for archived event cards
• Show “archived” label/badge on archived events
• Disable editing of archived events
• Add toggle or filter in event list: All | Active | Archived (TBC)
• Optional: dim or gray out archived events in the list (if shown)

Notes

• Archiving should be soft: no data is lost
• This feature helps preserve historical context without cluttering the UI or analytics