feat: auto-save 2s + indicateur save + reminders inline actions (compléter/snooze)

- Auto-save debounce 2s dans note-editor-context
- lastSavedAt state + setIsDirty(false) dans handleSave
- Indicateur toolbar: ✓ sauvegardé / ● non enregistré avec timer relatif
- Reminders sidebar: bouton ✓ compléter + bouton +1h snooze (hover inline)
- i18n: clés reminders.markDone/snooze1h + notes.savedJustNow/unsaved (15 locales)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

memento-note/locales/it.json

@@ -280,7 +280,9 @@
     "saveFailed": "Salvataggio non riuscito",
     "search": "Cerca",
     "unarchived": "Dearchiviato",
-    "uploading": "Caricamento..."
+    "uploading": "Caricamento...",
+    "savedJustNow": "Saved",
+    "unsaved": "Unsaved changes"
   },
   "pagination": {
     "previous": "←",
@@ -1011,7 +1013,8 @@
     "todayAt": "Oggi alle {time}",
     "tomorrowAt": "Domani alle {time}",
     "clearCompleted": "Cancella completato",
-    "viewAll": "Visualizza tutti i promemoria"
+    "viewAll": "Visualizza tutti i promemoria",
+    "snooze1h": "Snooze 1 hour"
   },
   "notebook": {
     "create": "Crea notebook",