feat(widgets): wire up tabbed app editing in widget edit modal

- Add hideButtons/formRef props to AppForm for headless embedding
- Add Mantine Tabs to WidgetEditModal for app widgets (permission-gated)
- Pass appId from BoardItemMenu to the modal
- Add translation keys for tab labels and propagation notice

apps/nextjs/src/components/board/items/item-menu.tsx

@@ -85,6 +85,7 @@ const BoardItemMenuInner = ({ offset, item, resetErrorBoundary }: BoardItemMenuP
         ),
         integrationSupport: "supportedIntegrations" in currentDefinition,
         settings,
+        appId: item.kind === "app" ? (item.options.appId as string | undefined) : undefined,
       },
       {
         title(t) {