feat: bloc Toggle/Section repliable + infrastructure embeddings par fragments

- Nouveau bloc Toggle : sections dépliables dans l'éditeur (slash menu + drag handle)
  - Transformer un bloc existant en section repliable via le menu d'action
  - Boutons désactiver (unwrap) et supprimer dans l'en-tête
  - i18n FR/EN complet
- Infrastructure embeddings par fragments (inspiré AppFlowy)
  - Table NoteEmbeddingChunk + index HNSW
  - Chunking sémantique (~1000 chars, overlap 200, dedup par hash)
  - Indexation incrémentale au save (createNote + updateNote + clip)
  - Queue concurrence 4, retry backoff exponentiel

memento-note/components/block-action-menu.tsx

@@ -14,8 +14,10 @@ import {
   Heading1, Heading2, Heading3, List, ListOrdered,
   CheckSquare, Quote, CodeXml, Database,
   ArrowUp, ArrowDown, AlignLeft, ClipboardCopy, Sparkles,
+  ChevronsRightLeft,
 } from 'lucide-react'
 import { replaceBlockWithStructuredView } from '@/components/tiptap-structured-view-block-extension'
+import { insertToggleBlock, turnIntoToggleBlock } from '@/components/tiptap-toggle-extension'
 
 interface BlockActionMenuProps {
   editor: Editor
@@ -369,6 +371,14 @@ export function BlockActionMenu({
 
       <div className="block-action-separator" />
 
+      {/* Section repliable */}
+      <button type="button" className="block-action-item" onClick={() => { turnIntoToggleBlock(editor, blockPos, blockNode); onClose() }}>
+        <ChevronsRightLeft size={16} />
+        <span>{t('richTextEditor.blockActionInsertToggle')}</span>
+      </button>
+
+      <div className="block-action-separator" />
+
       {/* Création de diagramme */}
       <button type="button" className="block-action-item" onClick={() => { void handleCreateDiagram() }}>
         <Sparkles size={16} className="text-amber-500 transition-all duration-200" />