feat: chunks recherche (snippets) + script migration

1. Recherche: fetchChunkSnippets() — après le classement RRF existant,
   récupère les passages précis qui matchent depuis NoteEmbeddingChunk.
   Pur affichage, AUCUN changement de classement.

2. Script migration: scripts/migrate-chunk-embeddings.ts
   Indexe toutes les notes existantes en fragments.
   Batch de 10, barre de progression.
   Usage: npx tsx scripts/migrate-chunk-embeddings.ts

3. Memory Echo chunk-level: à faire (US restante)

memento-note/components/rich-text-editor.tsx

@@ -3,6 +3,7 @@
 import { useEffect, useRef, useState, useCallback, forwardRef, useImperativeHandle } from 'react'
 import { createPortal } from 'react-dom'
 import { useLanguage } from '@/lib/i18n'
+import { sanitizeRichHtml } from '@/lib/sanitize-content'
 import { useEditor, EditorContent, useEditorState } from '@tiptap/react'
 import { BubbleMenu } from '@tiptap/react/menus'
 import StarterKit from '@tiptap/starter-kit'
@@ -1572,7 +1573,7 @@ function BubbleToolbar({ editor, onSuggestCharts }: { editor: Editor | null; onS
             )}
             <div className="notion-ai-result-section">
               {aiModal.type === 'preview' && <span className="notion-ai-result-label">{t('ai.result.suggestion') || 'Suggestion'}</span>}
-              <div className="prose prose-sm max-w-none text-sm mt-1" dangerouslySetInnerHTML={{ __html: aiModal.html }} />
+              <div className="prose prose-sm max-w-none text-sm mt-1" dangerouslySetInnerHTML={{ __html: sanitizeRichHtml(aiModal.html) }} />
             </div>
             <div className="flex justify-end gap-2 mt-3 pt-3 border-t border-border/40">
               <button onClick={() => setAiModal(null)} className="notion-modal-btn">{t('common.cancel') || 'Annuler'}</button>