fix(clipboard): add support for notion and github-flavored markdown checklist formats

- detect `to-do-list` (Notion) and `task-list` (GitHub MD) classes as checklist containers
- handle notion `<div class="checkbox-on/off">` as checkbox indicator in list items
- update README to document newly recognized HTML tags for checklist input

src/shared/components/BlockEditor/README.md

@@ -244,7 +244,7 @@ Le presse-papier transporte deux MIME en parallèle : `text/html` (structure
   sélectionnés.
 
 Tags HTML reconnus en entrée : `<h1>`–`<h6>`, `<p>`, `<ul>/<ol><li>`,
-`<ul data-checklist>` ou `<li>` contenant `<input type="checkbox">`,
+`<ul data-checklist>`, `<ul class="to-do-list">` (Notion), `<ul class="task-list">` (GitHub-flavored markdown), ou `<li>` contenant `<input type="checkbox">` ou `<div class="checkbox checkbox-on/off">` (Notion),
 `<blockquote>`, `<pre>`, `<code>`, `<hr>`, `<figure>`, `<img>`, plus
 toutes les marks de `domToInline` (`<strong>/<b>`, `<em>/<i>`, `<u>`,
 `<s>/<strike>/<del>`, `<code>`, `<a href>`, `<span data-color>` /