feat: AI Overview recherche + AI Writer inline streaming

- AI Overview : synthèse IA en haut des résultats de recherche (Ctrl+K)
  - Service search-overview.service.ts
  - Endpoint /api/ai/search-overview
  - Carte 'Réponse IA' avec Sparkles en haut du panneau gauche
  - Pur additif, ne modifie pas le classement des résultats
- AI Writer inline : slash menu → 'Écrire avec l'IA' → champ inline
  - Mode 'write' dans paragraph-refactor.service.ts
  - Streaming paragraphe par paragraphe (120ms delay)
  - Nettoyage HTML (espaces vides supprimés)
  - Ref synchrone pour éviter fermeture du menu pendant la frappe
- Fix: index slashCommands AI Writer corrigé
- Fix: Loader2 import manquant
- i18n FR/EN

memento-note/components/sidebar.tsx

@@ -632,6 +632,8 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
   const [trashCount, setTrashCount] = useState(0)
 
   const [draggedId, setDraggedId] = useState<string | null>(null)
+  // Ref stable pour éviter les stale closures dans les handlers de drop
+  const draggedIdRef = useRef<string | null>(null)
   const [orderedNotebooks, setOrderedNotebooks] = useState<Notebook[]>([])
   const dragOverId = useRef<string | null>(null)
   const isSavingRef = useRef(false)
@@ -852,61 +854,85 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
 
   // ── Drag state ──
   const [dropTarget, setDropTarget] = useState<string | null>(null)
-  const [dropAction, setDropAction] = useState<'into' | null>(null)
+  const [dropAction, setDropAction] = useState<'into' | 'before' | 'after' | null>(null)
 
-  const handleDragStart = (e: React.DragEvent, notebookId: string) => {
+  const handleDragStart = useCallback((e: React.DragEvent, notebookId: string) => {
+    // Stocker dans le ref ET dans le state
+    // Le ref est toujours frais dans les handlers async (pas de stale closure)
+    draggedIdRef.current = notebookId
     setDraggedId(notebookId)
     e.dataTransfer.effectAllowed = 'move'
     e.dataTransfer.setData('text/plain', notebookId)
-  }
+  }, [])
 
-  const handleDragEnd = () => {
+  const handleDragEnd = useCallback(() => {
+    draggedIdRef.current = null
     setDraggedId(null)
     dragOverId.current = null
     isSavingRef.current = false
     setDropTarget(null)
     setDropAction(null)
     setOrderedNotebooks(sortedNotebooks)
-  }
+  }, [sortedNotebooks])
 
-  const handleDropOnNotebook = async (e: React.DragEvent, targetId: string) => {
+  const handleDropOnNotebook = useCallback(async (e: React.DragEvent, targetId: string, action: 'into' | 'before' | 'after') => {
     e.preventDefault()
     e.stopPropagation()
+    const dragId = draggedIdRef.current || e.dataTransfer.getData('text/plain')
+    draggedIdRef.current = null
+    setDraggedId(null)
     setDropTarget(null)
     setDropAction(null)
-    const dragId = draggedId || e.dataTransfer.getData('text/plain')
-    if (!dragId || dragId === targetId) {
-      setDraggedId(null)
-      return
-    }
-    setDraggedId(null)
     dragOverId.current = null
+    if (!dragId || dragId === targetId) return
     try {
-      await moveNotebookToParent(dragId, targetId)
+      if (action === 'into') {
+        await moveNotebookToParent(dragId, targetId)
+      } else {
+        // before/after : placer au même niveau que la cible et réordonner
+        const target = orderedNotebooks.find(nb => nb.id === targetId)
+        const newParentId = target?.parentId ?? null
+
+        // 1. Mettre à jour le parentId si nécessaire
+        const dragged = orderedNotebooks.find(nb => nb.id === dragId)
+        if (dragged?.parentId !== newParentId) {
+          await moveNotebookToParent(dragId, newParentId)
+        }
+
+        // 2. Recalculer l'ordre des siblings
+        const siblings = orderedNotebooks
+          .filter(nb => (nb.parentId ?? null) === newParentId && nb.id !== dragId)
+        const targetIdx = siblings.findIndex(nb => nb.id === targetId)
+        const insertAt = action === 'before' ? targetIdx : targetIdx + 1
+        siblings.splice(insertAt, 0, { id: dragId } as typeof siblings[0])
+        // Passer en tri manuel pour que l'ordre soit respecté visuellement
+        setSortOrder('manual')
+        await updateNotebookOrderOptimistic(siblings.map(nb => nb.id))
+      }
     } catch (err) {
       toast.error(err instanceof Error ? err.message : t('sidebar.moveFailed'))
       setOrderedNotebooks(sortedNotebooks)
     }
-  }
+  }, [moveNotebookToParent, updateNotebookOrderOptimistic, orderedNotebooks, sortedNotebooks, t])
 
-  const handleDropToRoot = async (e: React.DragEvent) => {
+  const handleDropToRoot = useCallback(async (e: React.DragEvent) => {
     e.preventDefault()
+    // Lire depuis le ref (toujours à jour, pas de stale closure)
+    const dragId = draggedIdRef.current || e.dataTransfer.getData('text/plain')
+    // Nettoyer APRÈS avoir lu la valeur
+    draggedIdRef.current = null
+    setDraggedId(null)
     setDropTarget(null)
     setDropAction(null)
-    const dragId = draggedId || e.dataTransfer.getData('text/plain')
-    if (!dragId) {
-      setDraggedId(null)
-      return
-    }
-    setDraggedId(null)
     dragOverId.current = null
+    if (!dragId) return
     try {
       await moveNotebookToParent(dragId, null)
     } catch (err) {
       toast.error(err instanceof Error ? err.message : t('sidebar.moveFailed'))
       setOrderedNotebooks(sortedNotebooks)
     }
-  }
+  }, [moveNotebookToParent, sortedNotebooks, t])
 
   const sortLabels: Record<SortOrder, string> = {
     newest: t('sidebar.sortNewest'),
@@ -1033,8 +1059,13 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
               e.stopPropagation()
               if (!draggedId || draggedId === notebook.id) return
               e.dataTransfer.dropEffect = 'move'
+              const rect = e.currentTarget.getBoundingClientRect()
+              const y = e.clientY - rect.top
+              const pct = y / rect.height
               setDropTarget(notebook.id)
-              setDropAction('into')
+              if (pct < 0.3) setDropAction('before')
+              else if (pct > 0.7) setDropAction('after')
+              else setDropAction('into')
             }}
             onDragLeave={(e) => {
               if (e.currentTarget.contains(e.relatedTarget as Node)) return
@@ -1046,15 +1077,24 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
             onDrop={(e) => {
               e.preventDefault()
               e.stopPropagation()
-              handleDropOnNotebook(e, notebook.id)
+              const action = (dropTarget === notebook.id ? dropAction : null) ?? 'into'
+              handleDropOnNotebook(e, notebook.id, action as 'into' | 'before' | 'after')
             }}
             className={cn(
-              'rounded-lg transition-colors',
+              'relative rounded-lg transition-colors',
               dropTarget === notebook.id && dropAction === 'into' && draggedId && draggedId !== notebook.id
                 && 'bg-brand-accent/10 ring-1 ring-brand-accent/30',
               isDragging && 'opacity-50'
             )}
           >
+            {/* Indicateur "déposer avant" */}
+            {dropTarget === notebook.id && dropAction === 'before' && draggedId && draggedId !== notebook.id && (
+              <div className="absolute -top-0.5 start-0 end-0 h-0.5 bg-brand-accent rounded-full z-10 pointer-events-none" />
+            )}
+            {/* Indicateur "déposer après" */}
+            {dropTarget === notebook.id && dropAction === 'after' && draggedId && draggedId !== notebook.id && (
+              <div className="absolute -bottom-0.5 start-0 end-0 h-0.5 bg-brand-accent rounded-full z-10 pointer-events-none" />
+            )}
             <SidebarCarnetItem
               carnet={{
                 id: notebook.id,
@@ -1481,17 +1521,27 @@ export function Sidebar({ className, user }: { className?: string; user?: any })
 
                   <div className="my-3 h-px bg-border/40" />
 
+                  {/* Zone de dépôt racine — toujours présente pour éviter tout décalage DOM */}
+                  <div
+                    className={`mb-2 h-10 rounded-lg border-2 border-dashed flex items-center justify-center gap-2 text-[11px] font-medium transition-all duration-150 ${
+                      draggedId
+                        ? 'border-brand-accent/40 bg-brand-accent/5 text-brand-accent/70 opacity-100 cursor-copy pointer-events-auto'
+                        : 'border-transparent bg-transparent text-transparent opacity-0 pointer-events-none'
+                    }`}
+                    onDrop={handleDropToRoot}
+                    onDragOver={(e) => { e.preventDefault(); e.stopPropagation() }}
+                    onDragEnter={(e) => { e.preventDefault() }}
+                  >
+                    <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5" strokeLinecap="round" strokeLinejoin="round"><path d="M3 9l9-7 9 7v11a2 2 0 01-2 2H5a2 2 0 01-2-2z"/><polyline points="9 22 9 12 15 12 15 22"/></svg>
+                    {t('sidebar.dropToRoot')}
+                  </div>
+
                   <div
                     className="space-y-0.5 min-h-[60px]"
                     onDrop={handleDropToRoot}
                     onDragOver={(e) => e.preventDefault()}
                   >
                     {renderCarnetTree(undefined, 0)}
-                    {draggedId && (
-                      <div className="h-10 rounded-lg border-2 border-dashed border-brand-accent/20 flex items-center justify-center text-[11px] text-brand-accent/50">
-                        {t('sidebar.dropToRoot')}
-                      </div>
-                    )}
                   </div>
                 </div>
               </motion.div>