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/main.py

@@ -39,13 +39,13 @@ async def lifespan(_app: FastAPI):
             (admin_hash,)
         )
         conn.commit()
-    logger.info("FlowDeck v4.7.0 started on port %d", settings.app_port)
+    logger.info("FlowDeck v4.7.1 started on port %d", settings.app_port)
     yield
 
 
 app = FastAPI(
     title="FlowDeck",
-    version="4.7.0",
+    version="4.7.1",
     docs_url="/docs" if settings.log_level == "DEBUG" else None,
     redoc_url=None,
     lifespan=lifespan,