refactor!: replace Zustand global store with TanStack Query for systemFeatures

Follow-up to SSR prefetch migration (2833965). Eliminates the Zustand
middleman that was syncing TanStack Query data into a separate store.

- Remove useGlobalPublicStore Zustand store entirely
- Create hooks/use-global-public.ts with useSystemFeatures,
  useSystemFeaturesQuery, useIsSystemFeaturesPending, useSetupStatusQuery
- Migrate all 93 consumers to import from @/hooks/use-global-public
- Simplify global-public-context.tsx to a thin provider component
- Update 18 test files to mock the new hook interface
- Fix SetupStatusResponse.setup_at type from Date to string (JSON)
- Fix setup-status.spec.ts mock target to match consoleClient

BREAKING CHANGE: useGlobalPublicStore is removed. Use useSystemFeatures()
from @/hooks/use-global-public instead.

web/app/components/plugins/plugin-detail-panel/operation-dropdown.spec.tsx

@@ -11,8 +11,7 @@ vi.mock('react-i18next', () => ({
 }))
 
 vi.mock('@/context/global-public-context', () => ({
-  useGlobalPublicStore: <T,>(selector: (state: { systemFeatures: { enable_marketplace: boolean } }) => T): T =>
-    selector({ systemFeatures: { enable_marketplace: true } }),
+  useSystemFeatures: () => ({ enable_marketplace: true }),
 }))
 
 vi.mock('@/utils/classnames', () => ({