fix: label management - transaction safety, deletion sync, error handling

- Use prisma.$transaction in auto-label-creation.service with tx client
- Fix DELETE /api/labels to properly JSON.parse + disconnect labelRelations
- Fix PUT /api/labels rename to handle JSON labels
- Graceful error handling in /api/ai/tags and /api/ai/auto-labels
- Client-side label-deleted event in home-client, notes-tabs-view, label-management-dialog

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/components/notes-tabs-view.tsx

@@ -325,6 +325,24 @@ export function NotesTabsView({ notes, onEdit, currentNotebookId }: NotesTabsVie
     )
   }, [items])
 
+  // Listen for global label deletion and immediately update local state
+  useEffect(() => {
+    const handler = (e: Event) => {
+      const { name } = (e as CustomEvent).detail
+      if (!name) return
+      setItems((prev) =>
+        prev.map((note) => {
+          const currentLabels = note.labels || []
+          const updated = currentLabels.filter((l) => l.toLowerCase() !== name.toLowerCase())
+          if (updated.length === currentLabels.length) return note
+          return { ...note, labels: updated.length > 0 ? updated : null }
+        })
+      )
+    }
+    window.addEventListener('label-deleted', handler)
+    return () => window.removeEventListener('label-deleted', handler)
+  }, [])
+
   // Scroll to top of sidebar on note change handled by NoteInlineEditor internally
 
   const sensors = useSensors(