feat(phase-4-09): wire components into views — sidebar, cards, home, folder, shared, settings, admin

- AppSidebar: add 'Shared with me' entry (purple icon, count badge) and Folders section with New folder CTA
- DocumentCard: add group class, hover-reveal share button, ShareModal v-if, shared indicator pill
- HomeView: add SearchBar + SortControls above document list; fetchFolders on mount
- FolderView: new view with FolderBreadcrumb, FolderRow list, inline new-subfolder input, document list
- SharedView: new view fetching /api/shares/received with owner_handle display and empty state
- DocumentView: add PDF preview logic (in_app=DocumentPreviewModal, new_tab=window.open); load preferences on mount
- SettingsView: add Document Preferences card with pdf_open_mode radio buttons, auto-save on change
- AdminView: add Audit Log tab alongside Users/Quotas/AI Config tabs

frontend/src/views/AdminView.vue

@@ -21,6 +21,7 @@
     <AdminUsersTab v-if="activeTab === 'users'" />
     <AdminQuotasTab v-if="activeTab === 'quotas'" />
     <AdminAiConfigTab v-if="activeTab === 'ai'" />
+    <AuditLogTab v-if="activeTab === 'audit'" />
   </div>
 </template>
 
@@ -29,11 +30,13 @@ import { ref } from 'vue'
 import AdminUsersTab from '../components/admin/AdminUsersTab.vue'
 import AdminQuotasTab from '../components/admin/AdminQuotasTab.vue'
 import AdminAiConfigTab from '../components/admin/AdminAiConfigTab.vue'
+import AuditLogTab from '../components/admin/AuditLogTab.vue'
 
 const tabs = [
   { id: 'users', label: 'Users' },
   { id: 'quotas', label: 'Quotas' },
   { id: 'ai', label: 'AI Config' },
+  { id: 'audit', label: 'Audit Log' },
 ]
 
 const activeTab = ref('users')