Simplify event date initialization in event form.

Ensure the event date is formatted to 'YYYY-MM-DD' when pre-filling the form. This prevents potential issues with date handling and improves consistency in date rendering.

frontend/src/components/events/event-form.tsx

@@ -57,7 +57,7 @@ export function EventForm({
     location_name: event?.location_name || "",
     location_address: event?.location_address || "",
     location_url: event?.location_url || "",
-    event_date: event?.event_date || "",
+    event_date: event?.event_date ? event.event_date.substring(0, 10) : "",
     event_start_time: event?.event_start_time || "",
     event_end_time: event?.event_end_time || "",
     timezone: event?.timezone || "UTC",