fix(editor): v4.7.1 popovers Share/More/Activity/Move rendus sous le viewport + sous-menu Export inatteignable

- share-dialog/more-menu/activity-popover/move-dialog: enfants de .page-editor-wrapper
  (overflow-y:auto) ancores en absolute top:100% -> invisibles sous le viewport.
  Repositionnes en fixed sous la topbar, scope .page-editor-wrapper > (pas de
  regression sur .more-menu de library/local_workspace) + variante mobile <768px.
- Item Export du menu More faisait moreOpen=false avant d'ouvrir exportOpen:
  les 4 formats etaient inaccessibles. Devient un toggle, le menu reste ouvert.
- Cache busting app.css v=4.7.1; VERSION/main.py bump 4.7.1; CHANGELOG+ROADMAP a jour.
- Verifie Playwright headless: Share/More/Export/download Markdown/toast OK, 0 pageerror; 190/190 tests.

app/templates/base.html

@@ -5,7 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>FlowDeck — {% block title_prefix %}Home{% endblock %}</title>
   <link rel="icon" type="image/svg+xml" href="/static/favicon.svg">
-  <link rel="stylesheet" href="/static/css/app.css?v=3.0.0">
+  <link rel="stylesheet" href="/static/css/app.css?v=4.7.1">
   <link rel="stylesheet" href="/static/css/katex.min.css?v=0.16.11">
   <style>
     /* ── Mobile responsive (v4.0.2) ── */