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/_page_editor_content.html

@@ -345,7 +345,7 @@
                 @click.outside="!_justOpened && (moreOpen = false)"
                 x-transition
             >
-                <div class="more-menu-item" @click="moreOpen = false; exportOpen = true">↗ Export</div>
+                <div class="more-menu-item" @click="exportOpen = !exportOpen">↗ Export <span style="margin-left:auto;font-size:10px;opacity:.6">▾</span></div>
                 <template x-if="exportOpen">
                   <div class="more-menu-sub">
                     <div class="more-menu-item" @click="exportPage('markdown')"> Markdown (.md)</div>