fix: make conferencing provider optional during batch creation

The conferencing_provider Select field defaulted to "Zoom" (first option)
when not explicitly set, causing batch creation to fail with
"Please select a Zoom account for this batch" since no zoom_account
is provided at creation time.

frontend/src/pages/Batches/BatchForm.vue

@@ -483,6 +483,10 @@ const trashBatch = (close) => {
 
 const conferencingOptions = computed(() => {
 	return [
+		{
+			label: '',
+			value: '',
+		},
 		{
 			label: 'Zoom',
 			value: 'Zoom',

lms/lms/doctype/lms_batch/lms_batch.json

@@ -366,7 +366,7 @@
    "fieldname": "conferencing_provider",
    "fieldtype": "Select",
    "label": "Conferencing Provider",
-   "options": "Zoom\nGoogle Meet"
+   "options": "\nZoom\nGoogle Meet"
   },
   {
    "depends_on": "eval:doc.conferencing_provider=='Zoom'",