Fix event_conclusion_message being stored as [object Object] in database

- Removed duplicate FormData.append() call for event_conclusion_message
- The field was being appended twice: once in the forEach loop and once explicitly
- This caused the backend to receive malformed data resulting in [object Object]
- Now the field is only appended once through the normal form processing loop

frontend/src/components/EventForm.tsx

@@ -128,9 +128,6 @@ const EventForm: React.FC = () => {
         }
       });
 
-      // Append event conclusion message
-      submitData.append('event_conclusion_message', String(formData.event_conclusion_message)); // Ensure it's a string
-
 
       // Append wallpaper if selected
       if (wallpaper) {