Keep the stored stacks and filters when editing a workflow

editWorkflow() filled the form and then called onBoardChange() to populate
the dependent dropdowns -- but that function exists to *reset* them, so it
immediately nulled sourceStackId, targetStackId and both filter lists again.
The board stayed selected because it is not one of the fields it clears.

Split the two responsibilities: loadBoardOptions() only fetches the
stack/label/user lists, onBoardChange() clears the dependent selection and
then delegates to it. Editing now calls loadBoardOptions() directly.

onBoardChange() additionally ignores re-picking the board that is already
loaded, so selecting the same entry again no longer wipes the form.

src/PersonalSettings.vue

@@ -164,6 +164,8 @@ const editingId = ref(null)
 const stackOptions = ref([])
 const labelOptions = ref([])
 const participantOptions = ref([])
+// Which board the three lists above currently belong to.
+const loadedBoardId = ref(null)
 
 const boardOptions = computed(() => boards.value.map((board) => ({ value: board.id, label: board.title })))
 
@@ -223,14 +225,16 @@ async function loadAll() {
 	}
 }
 
-async function onBoardChange(boardId) {
+/**
-	form.sourceStackId = null
+ * Fills the stack/label/user dropdowns for a board without touching the
-	form.targetStackId = null
+ * current selection — that separation matters: editing a workflow has to
-	form.filterUserIds = []
+ * load the same options but must keep the stored stacks and filters.
-	form.filterLabelIds = []
+ */
+async function loadBoardOptions(boardId) {
 	stackOptions.value = []
 	labelOptions.value = []
 	participantOptions.value = []
+	loadedBoardId.value = boardId ?? null
 
 	if (!boardId) {
 		return
@@ -249,13 +253,29 @@ async function onBoardChange(boardId) {
 	participantOptions.value = participants.map((participant) => ({ value: participant.uid, label: participant.displayName }))
 }
 
+/**
+ * Only for the board dropdown: a *different* board invalidates everything
+ * that referenced the old one. Re-picking the same board is a no-op, so it
+ * doesn't silently wipe the form.
+ */
+async function onBoardChange(boardId) {
+	if (boardId === loadedBoardId.value) {
+		return
+	}
+
+	form.sourceStackId = null
+	form.targetStackId = null
+	form.filterUserIds = []
+	form.filterLabelIds = []
+
+	await loadBoardOptions(boardId)
+}
+
 function startCreate() {
 	Object.assign(form, emptyForm())
 	editingId.value = null
 	formError.value = ''
-	stackOptions.value = []
+	loadBoardOptions(null)
-	labelOptions.value = []
-	participantOptions.value = []
 	showForm.value = true
 }
 
@@ -273,7 +293,7 @@ async function editWorkflow(workflow) {
 	editingId.value = workflow.id
 	formError.value = ''
 	showForm.value = true
-	await onBoardChange(workflow.boardId)
+	await loadBoardOptions(workflow.boardId)
 }
 
 function cancelForm() {