🩹 round event end time to nearest minute

Ensures that the event end time is rounded down to the nearest minute.

This prevents potential collision issues where events start and end at
very close times (seconds/milliseconds), especially when creating new events.

src/booking.py

@@ -176,6 +176,9 @@ class Event(models.Model):
             self.created = datetime.now(tz=timezone.get_current_timezone())
         self.ics = self.create_ics()
 
+        # Round down to the nearest minute to avoid collisions between events
+        self.end = self.end.replace(second=0, microsecond=0)
+
         # Send the event to the CalDAV server if it has not been cancelled yet
         if not self.cancelled:
             try: