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.

static/css/app.css

@@ -2997,6 +2997,37 @@ button.breadcrumb-current { max-width: 260px; }
   border-radius: var(--radius-lg); box-shadow: var(--shadow-modal);
   z-index: 999;
 }
+/* Page editor: these popovers are children of .page-editor-wrapper (a scroll
+   container), so absolute top:100% anchored them BELOW the viewport. Pin them
+   fixed under the topbar instead. Scoped to the editor wrapper so other pages
+   (library, local_workspace) keep their relative-positioned .more-menu. */
+.page-editor-wrapper > .share-dialog,
+.page-editor-wrapper > .more-menu,
+.page-editor-wrapper > .activity-popover,
+.page-editor-wrapper > .move-dialog {
+  position: fixed !important;
+  top: calc(var(--topbar-height) + 6px) !important;
+}
+.page-editor-wrapper > .share-dialog { right: 72px; }
+.page-editor-wrapper > .more-menu { right: 16px; }
+.page-editor-wrapper > .activity-popover,
+.page-editor-wrapper > .move-dialog { right: 16px !important; }
+@media (max-width: 768px) {
+  /* Keep editor popovers centered/stacked on mobile (base.html media rule
+     uses !important; mirror the specificity so it still wins here). */
+  .page-editor-wrapper > .share-dialog,
+  .page-editor-wrapper > .more-menu,
+  .page-editor-wrapper > .activity-popover,
+  .page-editor-wrapper > .move-dialog {
+    right: auto !important;
+    top: 50% !important;
+    width: 92vw !important;
+    max-width: 400px;
+    transform: translate(-50%, -50%) !important;
+  }
+  .page-editor-wrapper > .more-menu,
+  .page-editor-wrapper > .activity-popover { top: 60px !important; transform: none !important; left: auto !important; right: 12px !important; width: auto !important; }
+}
 /* Header with tabs */
 .sd-header {
   display: flex; align-items: center; height: 56px;