feat: icon-only toolbar, versioning fixes, history modal, PanelRight repositioning

- Toolbar: remove text labels from all icon buttons (AI, Save, Preview, Convert)
  all buttons now icon-only with title tooltip for accessibility
- Toolbar: reposition PanelRight (info panel toggle) to far right after three-dot menu
- Versioning: decouple getNoteHistory/restoreNoteVersion from global userAISettings.noteHistory
  now checks note.historyEnabled directly — unblocks manual per-note history
- Versioning: add 'Sauvegarder cette version' button in Versions tab of info panel
  calls commitNoteHistory with visual feedback (spinner → success state)
- note-document-info-panel: import commitNoteHistory, add isSavingVersion state
- notes.ts: fix double guard that silently blocked all history operations

memento-note/app/(admin)/admin/layout.tsx

@@ -1,29 +1,21 @@
-import { AdminHeader } from '@/components/admin-header'
-import { AdminNav } from '@/components/admin-nav'
+import { AdminSidebar } from '@/components/admin-sidebar'
 
 // Auth is enforced solely by middleware (auth.config.ts → authorized callback).
-// All cross-group navigation (admin ↔ main) uses <a> tags (full page reload)
-// to avoid React Error #310 caused by Next.js 16.x route-group transition bug.
+// Navigation admin ↔ app en <a> (rechargement complet) pour éviter React Error #310
+// sur les transitions entre route groups (Next.js 16 / React #33580).
 export default function AdminLayout({
   children,
 }: {
   children: React.ReactNode
 }) {
   return (
-    <div className="bg-background flex flex-col min-h-screen">
-      <AdminHeader />
-      
-      {/* Horizontal Tab Navigation */}
-      <div className="flex items-center gap-1 px-8 bg-background border-b border-border shrink-0">
-        <AdminNav />
-      </div>
-
-      {/* Page Content */}
-      <div className="flex-1 overflow-y-auto">
-        <div className="max-w-5xl mx-auto px-8 py-8 space-y-8">
+    <div className="flex h-screen overflow-hidden bg-[#E5E2D9] dark:bg-background">
+      <AdminSidebar />
+      <main className="memento-paper-texture flex min-h-0 flex-1 flex-col overflow-y-auto scroll-smooth">
+        <div className="mx-auto w-full max-w-6xl space-y-8 px-4 py-6 sm:px-6 sm:py-8 lg:px-10">
           {children}
         </div>
-      </div>
+      </main>
     </div>
   )
 }