Handle workflows whose board or stack was deleted

Deleting a board or stack left the workflow row pointing at nothing: Deck
keeps the orphaned cards readable until its DeleteCron purges them, so the
run kept failing on the move every few minutes, silently and forever.

- The controller now rejects boards and stacks that do not exist (or are not
  the user's) on create and update, so no new broken row can be stored.
- The settings list marks affected workflows in red instead of showing a row
  that looks healthy.
- The background job disables such a workflow and mails its owner once. The
  mail ignores the notifyEmail flag: that one is about moved cards, this is a
  notice that the automation stopped. It stays a one-off because a disabled
  workflow is no longer picked up.

The check deliberately goes through StackService::findAll() rather than
BoardService::getUserBoards(): Deck injects the current user into BoardService
as a string frozen at construction, so in the job -- one process, many users,
a cached BoardService -- it would answer for the wrong user or for none, and
every workflow on the instance would have been disabled. findStackIds()
returns null only for a genuinely missing or forbidden board and throws for
anything else, so a Deck outage skips the workflow instead of killing it.

src/PersonalSettings.vue

@@ -25,7 +25,12 @@
 				</thead>
 				<tbody>
 					<tr v-for="workflow in workflows" :key="workflow.id">
-						<td>{{ workflow.title }}</td>
+						<td>
+							{{ workflow.title }}
+							<span v-if="workflowIssues[workflow.id]" class="wfda-issue">
+								{{ workflowIssues[workflow.id] }}
+							</span>
+						</td>
 						<td>{{ stackLabel(workflow.boardId, workflow.sourceStackId) }}</td>
 						<td>{{ stackLabel(workflow.boardId, workflow.targetStackId) }}</td>
 						<td>
@@ -175,6 +180,40 @@ const boardOptions = computed(() => boards.value.map((board) => ({ value: board.
 const sourceStackOptions = computed(() => stackOptions.value.filter((option) => option.value !== form.targetStackId))
 const targetStackOptions = computed(() => stackOptions.value.filter((option) => option.value !== form.sourceStackId))
 
+/**
+ * Workflows whose board or stacks were deleted in Deck, keyed by id. The
+ * background job switches these off by itself, but a row that just stopped
+ * working needs to say so instead of looking healthy.
+ */
+const workflowIssues = computed(() => {
+	const issues = {}
+
+	for (const workflow of workflows.value) {
+		if (!boards.value.some((board) => board.id === workflow.boardId)) {
+			issues[workflow.id] = 'Board nicht mehr vorhanden'
+			continue
+		}
+
+		const stacks = stacksByBoard[workflow.boardId]
+		if (!stacks) {
+			continue
+		}
+
+		const missing = []
+		if (!stacks.some((stack) => stack.id === workflow.sourceStackId)) {
+			missing.push('Quell-Stapel')
+		}
+		if (!stacks.some((stack) => stack.id === workflow.targetStackId)) {
+			missing.push('Ziel-Stapel')
+		}
+		if (missing.length) {
+			issues[workflow.id] = `${missing.join(' und ')} nicht mehr vorhanden`
+		}
+	}
+
+	return issues
+})
+
 const form = reactive(emptyForm())
 
 function emptyForm() {
@@ -370,6 +409,12 @@ onMounted(loadAll)
 	justify-content: flex-end;
 }
 
+.wfda-issue {
+	display: block;
+	color: var(--color-error);
+	font-size: 0.9em;
+}
+
 .wfda-empty {
 	color: var(--color-text-maxcontrast);
 	margin-bottom: 16px;