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/home-client.tsx

@@ -140,6 +140,24 @@ export function HomeClient({ initialNotes, initialSettings }: HomeClientProps) {
 
   useReminderCheck(notes)
 
+  // Listen for global label deletion and immediately update local state
+  useEffect(() => {
+    const handler = (e: Event) => {
+      const { name } = (e as CustomEvent).detail
+      if (!name) return
+      const removeLabel = (note: 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 }
+      }
+      setNotes((prev) => prev.map(removeLabel))
+      setPinnedNotes((prev) => prev.map(removeLabel))
+    }
+    window.addEventListener('label-deleted', handler)
+    return () => window.removeEventListener('label-deleted', handler)
+  }, [])
+
   const prevRefreshKey = useRef(refreshKey)
 
   // Rechargement uniquement pour les filtres actifs (search, labels, notebook)