feat: équations mathématiques (KaTeX) — bloc, inline, barre visuelle, IA

- Bloc équation avec barre visuelle 20 symboles (fractions, intégrales, grec, etc.)
- Math en ligne : tape $x^2$ → rendu KaTeX inline automatique
- Math en bloc : tape $$E=mc^2$$ → converti en bloc
- Génération IA : décrit l'équation en langage naturel → LaTeX
- Service math-from-text + endpoint /api/ai/math-from-text
- CSS KaTeX importé
- i18n FR/EN complet

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

@@ -31,6 +31,7 @@ import { CalloutExtension, insertCalloutBlock } from './tiptap-callout-extension
 import { OutlineExtension, insertOutlineBlock } from './tiptap-outline-extension'
 import { FindReplaceBar, FindReplaceExtension } from './editor-find-replace-bar'
 import { LinkPreviewExtension, insertLinkPreview, isUrl } from './tiptap-link-preview-extension'
+import { MathEquationExtension, InlineMathExtension, insertMathEquation } from './tiptap-math-extension'
 import { RtlPreserveExtension } from './tiptap-rtl-preserve-extension'
 import { ClipArticleExtension } from './tiptap-clip-article-extension'
 import { BlockPicker, type BlockSuggestion } from './block-picker'
@@ -67,7 +68,7 @@ import {
   FileText, Pilcrow, MessageSquare, AlignLeft, AlignCenter, AlignRight,
   Superscript as SuperscriptIcon, Subscript as SubscriptIcon, Expand, Plus,
   SpellCheck, Languages, BookOpen, Presentation, BarChart3, Database,
-  ChevronsRightLeft, MessageSquareWarning, ListTree
+  ChevronsRightLeft, MessageSquareWarning, ListTree, FunctionSquare
 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { toast } from 'sonner'
@@ -226,6 +227,10 @@ const slashCommands: SlashItem[] = [
       window.dispatchEvent(new CustomEvent('memento-open-link-preview'))
     },
   },
+  {
+    title: 'Math', description: 'LaTeX equation block', icon: FunctionSquare, category: 'Basic blocks', shortcut: '$$',
+    command: (e) => { insertMathEquation(e) },
+  },
 ]
 
 async function aiReformulate(text: string, option: string, t: any, language?: string): Promise<string> {
@@ -473,6 +478,8 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
         OutlineExtension,
         FindReplaceExtension,
         LinkPreviewExtension,
+        MathEquationExtension,
+        InlineMathExtension,
         ClipArticleExtension,
         RtlPreserveExtension,
         Placeholder.configure({
@@ -1695,6 +1702,7 @@ function SlashCommandMenu({ editor, onInsertImage, onSuggestCharts }: { editor:
     { ...slashCommands[32], title: t('richTextEditor.slashCallout'), description: t('richTextEditor.slashCalloutDesc'), categoryId: 'text', slashKeywords: ['callout', 'encadre', 'encadré', 'info', 'alerte', 'astuce', 'tip', 'warning'] },
     { ...slashCommands[33], title: t('richTextEditor.slashOutline'), description: t('richTextEditor.slashOutlineDesc'), categoryId: 'text', slashKeywords: ['outline', 'sommaire', 'toc', 'table', 'matieres', 'matières', 'plan'] },
     { ...slashCommands[34], title: t('richTextEditor.slashLinkPreview'), description: t('richTextEditor.slashLinkPreviewDesc'), categoryId: 'embed', slashKeywords: ['link', 'lien', 'url', 'preview', 'apercu', 'aperçu', 'embed', 'card', 'carte'] },
+    { ...slashCommands[35], title: t('richTextEditor.slashMath'), description: t('richTextEditor.slashMathDesc'), categoryId: 'text', slashKeywords: ['math', 'maths', 'equation', 'équation', 'formula', 'formule', 'latex', 'katex'] },
     {
       title: t('richTextEditor.slashNoteLink'),
       description: t('richTextEditor.slashNoteLinkDesc'),