fix: ensure slotDuration always has acceptable format

src/Pages/EmissionManager.vue

@@ -361,7 +361,7 @@ export default {
         select: this.createEvent,
         selectable: true,
         selectMirror: true,
-        slotDuration: `00:${slotDurationMinutes}:00`,
+        slotDuration: `00:${slotDurationMinutes.toString().padStart(2, '0')}:00`,
         eventMinHeight: 1,
         selectAllow({ start }) {
           return start >= getClosestSlot(slotDurationMinutes)