feat(06.2-05): actionable cloud error + audit log @ prefix

- CloudFolderView: detect no-connection error and show actionable message
  directing user to Settings; add router-link to /settings and Retry button
- AuditLogTab: prefix user handles with @ in the User column

frontend/src/components/admin/AuditLogTab.vue

@@ -92,7 +92,7 @@
             class="border-b border-gray-100 hover:bg-gray-50 transition-colors"
           >
             <td class="px-4 py-3 font-mono text-xs text-gray-500">{{ formatTimestamp(entry.created_at) }}</td>
-            <td class="px-4 py-3 text-sm text-gray-700">{{ entry.user_handle || entry.user_id || '—' }}</td>
+            <td class="px-4 py-3 text-sm text-gray-700">{{ entry.user_handle ? '@' + entry.user_handle : (entry.user_id || '—') }}</td>
             <td class="px-4 py-3">
               <span
                 class="text-xs px-2 py-1 rounded-full font-medium"

frontend/src/views/CloudFolderView.vue

@@ -34,8 +34,18 @@
       <div v-if="loading" class="text-sm text-gray-400 py-8 text-center">Loading…</div>
 
       <div v-else-if="error" class="text-sm text-red-500 py-8 text-center">
-        {{ error }}
-        <button @click="load" class="ml-2 text-indigo-600 hover:underline">Retry</button>
+        <p>{{ error }}</p>
+        <div class="flex items-center justify-center gap-3 mt-2">
+          <router-link
+            to="/settings"
+            class="text-indigo-600 hover:underline text-sm"
+          >
+            Go to Settings
+          </router-link>
+          <button @click="load" class="text-indigo-600 hover:underline text-sm">
+            Retry
+          </button>
+        </div>
       </div>
 
       <template v-else>
@@ -130,7 +140,12 @@ async function load() {
     const data = await api.getCloudFolders(provider.value, folderId.value ?? 'root')
     items.value = data.items ?? []
   } catch (e) {
-    error.value = e.message || 'Failed to load folder contents'
+    const msg = e.message || ''
+    if (msg.toLowerCase().includes('no active connection') || msg.includes('404') || msg.toLowerCase().includes('not found')) {
+      error.value = 'No cloud provider connected. Go to Settings to connect a cloud storage account.'
+    } else {
+      error.value = msg || 'Failed to load folder contents.'
+    }
   } finally {
     loading.value = false
   }