Event cover change: card thumbnail updates but the big cover stays the same

**What happens:** When an organizer changes an event's cover picture, the small thumbnail used on event cards updates correctly, but the large cover shown on the event detail page stays the old image. **Expected:** both should update — the big cover on the event detail page should match whatever was just uploaded, same as the card thumbnail does. **Where:** event detail page large cover image. Only reproduces on **production**. Dev environment behaves correctly (both sizes update as expected). **Repro:** 1. Sign in as an organizer of an event in production. 2. Open the event you want to edit. 3. Change the cover photo (upload a new image). 4. Confirm the upload succeeded. 5. Open the event card view (home, explore, group page, etc.) → the small thumbnail shows the new image ✓ 6. Open the event detail page → the large cover still shows the OLD image ✗ 7. Hard-reload doesn't fix it (cache check not the issue from the user's side).