docs: add comprehensive Stripe billing guide

Covers architecture, configuration steps, user flows, API routes,
webhooks, pricing, testing with Stripe CLI, production checklist,
and troubleshooting.

memento-note/components/note-actions.tsx

@@ -234,7 +234,7 @@ export function NoteActions({
             <DropdownMenuItem onClick={onOpenHistory}>
               <History className="h-4 w-4 mr-2" />
               {historyEnabled
-                ? (t('notes.history') || 'Historique')
+                ? t('notes.history')
                 : (t('notes.enableHistory') || "Activer l'historique")}
             </DropdownMenuItem>
           )}