fix(cloud): skeleton on first render + informative toast when opening cloud files

- loading initialised to true so skeleton rows show immediately on mount
  instead of the empty state flashing before data arrives
- @file-open no longer a silent no-op; shows an info toast explaining the
  file must be opened via the cloud provider directly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/CloudFolderView.vue

@@ -11,7 +11,7 @@
     @breadcrumb-navigate="handleBreadcrumbNavigate"
     @upload="onFilesSelected"
     @folder-navigate="item => navigateTo(item)"
-    @file-open="file => {}"
+    @file-open="onFileOpen"
   />
 </template>
 
@@ -21,12 +21,15 @@ import { useRoute, useRouter } from 'vue-router'
 import * as api from '../api/client.js'
 import StorageBrowser from '../components/storage/StorageBrowser.vue'
 import { providerLabel } from '../utils/formatters.js'
+import { useToastStore } from '../stores/toast.js'
 
 const route = useRoute()
 const router = useRouter()
 
+const toast = useToastStore()
+
 const items = ref([])
-const loading = ref(false)
+const loading = ref(true)
 const error = ref('')
 
 const provider = computed(() => route.params.provider)
@@ -92,6 +95,10 @@ async function onFilesSelected({ files: selectedFiles }) {
   await load()
 }
 
+function onFileOpen(file) {
+  toast.show(`"${file.name}" can't be opened here — open it directly in your cloud storage provider.`, 'info')
+}
+
 onMounted(load)
 watch([provider, folderId], load)
 </script>