perf: debounce getHTML() dans onUpdate — 400ms au lieu de chaque frappe

getHTML() traverse tout le document ProseMirror à chaque transaction.
Sur les notes longues (500+ blocs), cela causait des lags visibles.
Maintenant debounced à 400ms via setTimeout + clearTimeout.
Le wikilink detection reste synchrone (réactif).

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

@@ -359,12 +359,21 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
     const editorInstanceRef = useRef<Editor | null>(null)
     const onChangeRef = useRef(onChange)
     onChangeRef.current = onChange
+    const htmlDebounceRef = useRef<ReturnType<typeof setTimeout> | null>(null)
 
     const emitContentChange = useCallback((html: string) => {
       lastEmittedContent.current = html
       onChangeRef.current?.(html)
     }, [])
 
+    // Debounced version for onUpdate — avoids calling getHTML() on every keystroke
+    const emitContentChangeDebounced = useCallback((editor: any) => {
+      if (htmlDebounceRef.current) clearTimeout(htmlDebounceRef.current)
+      htmlDebounceRef.current = setTimeout(() => {
+        emitContentChange(editor.getHTML())
+      }, 400)
+    }, [emitContentChange])
+
     useEffect(() => {
       if (typeof window === 'undefined') return
       const checkMobile = () => setIsMobile(window.innerWidth < 768)
@@ -595,8 +604,8 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
         }
       },
       onUpdate: ({ editor: e }) => {
-        // Debounce getHTML() — it's expensive on long notes
+        // Debounced getHTML() — avoids traversing the whole doc on every keystroke
-        emitContentChange(e.getHTML())
+        emitContentChangeDebounced(e)
         if (!e.isEditable) return
         const { from, empty } = e.state.selection
         if (!empty) return