feat(gallery): add admin gallery curation endpoints and management page (Task 6)

Add super-admin-only backend endpoints for toggling is_gallery_featured and
gallery_sort_order on flows and scripts, plus a frontend GalleryManagementPage
with toggle switches, editable sort order fields, and name/featured filters.
13 integration tests; all pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/router.tsx

@@ -67,6 +67,7 @@ const AdminSettingsPage = lazy(() => import('@/pages/admin/SettingsPage'))
 const AdminGlobalCategoriesPage = lazy(() => import('@/pages/admin/GlobalCategoriesPage'))
 const AdminSurveyInvitesPage = lazy(() => import('@/pages/admin/SurveyInvitesPage'))
 const AdminSurveyResponsesPage = lazy(() => import('@/pages/admin/SurveyResponsesPage'))
+const AdminGalleryManagementPage = lazy(() => import('@/pages/admin/GalleryManagementPage'))
 
 // Account pages
 const AccountLayout = lazy(() => import('@/components/account/AccountLayout'))
@@ -210,6 +211,7 @@ export const router = sentryCreateBrowserRouter([
           { path: 'categories', element: page(AdminGlobalCategoriesPage) },
           { path: 'survey-invites', element: page(AdminSurveyInvitesPage) },
           { path: 'survey-responses', element: page(AdminSurveyResponsesPage) },
+          { path: 'gallery', element: page(AdminGalleryManagementPage) },
         ],
       },
       // Account routes