feat(05-08): add Cloud Storage collapsible section to AppSidebar

- Import CloudProviderTreeItem and useCloudConnectionsStore
- Add cloudExpanded ref (default true) and activeCloudConnections/loadingCloudConnections computed
- Insert Cloud Storage section between Folders and Topics sections
- Fetch connections on mount; render one CloudProviderTreeItem per ACTIVE connection
- Empty state: 'No cloud storage connected'; loading state: 'Loading...'

frontend/src/components/layout/AppSidebar.vue

@@ -110,6 +110,52 @@
         </template>
       </div>
 
+      <!-- Cloud Storage section -->
+      <div class="mt-3">
+        <div class="flex items-center gap-0.5">
+          <!-- Expand/collapse chevron -->
+          <button
+            @click="cloudExpanded = !cloudExpanded"
+            class="p-1 rounded hover:bg-gray-100 text-gray-400 hover:text-gray-600 transition-colors shrink-0"
+            :title="cloudExpanded ? 'Collapse cloud storage' : 'Expand cloud storage'"
+          >
+            <svg
+              class="w-3 h-3 transition-transform duration-150"
+              :class="cloudExpanded ? 'rotate-90' : ''"
+              fill="none" stroke="currentColor" viewBox="0 0 24 24"
+            >
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7" />
+            </svg>
+          </button>
+
+          <!-- "Cloud Storage" navigates to /settings -->
+          <a
+            href="/settings"
+            class="nav-link flex-1 min-w-0"
+          >
+            <svg class="w-4 h-4 mr-2 shrink-0 text-sky-500" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+              <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
+                d="M3 15a4 4 0 004 4h9a5 5 0 10-.1-9.999 5.002 5.002 0 10-9.78 2.096A4.001 4.001 0 003 15z" />
+            </svg>
+            Cloud Storage
+          </a>
+        </div>
+
+        <!-- Collapsible content -->
+        <template v-if="cloudExpanded">
+          <div v-if="loadingCloudConnections" class="pl-7 py-1 text-xs text-gray-400">Loading…</div>
+          <div v-else-if="activeCloudConnections.length === 0" class="pl-7 py-1 text-xs text-gray-400">
+            No cloud storage connected
+          </div>
+          <CloudProviderTreeItem
+            v-for="connection in activeCloudConnections"
+            :key="connection.id"
+            :connection="connection"
+            :depth="1"
+          />
+        </template>
+      </div>
+
       <!-- Topics list -->
       <div class="mt-3">
         <p class="px-3 text-xs font-semibold text-gray-400 uppercase tracking-wider mb-1">Topics</p>
@@ -186,18 +232,21 @@
 </template>
 
 <script setup>
-import { ref, onMounted, watch } from 'vue'
+import { ref, computed, onMounted, watch } from 'vue'
 import { useRouter } from 'vue-router'
 import { useTopicsStore } from '../../stores/topics.js'
 import { useAuthStore } from '../../stores/auth.js'
 import { useFoldersStore } from '../../stores/folders.js'
+import { useCloudConnectionsStore } from '../../stores/cloudConnections.js'
 import QuotaBar from './QuotaBar.vue'
 import FolderTreeItem from '../folders/FolderTreeItem.vue'
+import CloudProviderTreeItem from '../cloud/CloudProviderTreeItem.vue'
 import * as api from '../../api/client.js'
 
 const topicsStore = useTopicsStore()
 const authStore = useAuthStore()
 const foldersStore = useFoldersStore()
+const cloudConnectionsStore = useCloudConnectionsStore()
 const router = useRouter()
 
 const sharedCount = ref(0)
@@ -206,6 +255,12 @@ const newFolderName = ref('')
 const newFolderError = ref('')
 const loadingRoots = ref(true)
 const foldersExpanded = ref(false)
+const cloudExpanded = ref(true)
+
+const activeCloudConnections = computed(() =>
+  cloudConnectionsStore.connections.filter(c => c.status === 'ACTIVE')
+)
+const loadingCloudConnections = computed(() => cloudConnectionsStore.loading)
 
 watch(() => foldersStore.treeVersion, () => foldersStore.fetchRootFolders())
 
@@ -222,6 +277,7 @@ onMounted(async () => {
   } catch {
     sharedCount.value = 0
   }
+  cloudConnectionsStore.fetchConnections()
 })
 
 async function signOut() {