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-page/empty/index.spec.tsx

@@ -56,14 +56,10 @@ vi.mock('../context', () => ({
 
 // Mock global public store (Zustand store)
 vi.mock('@/context/global-public-context', () => ({
-  useGlobalPublicStore: (selector: (state: any) => any) => {
-    return selector({
-      systemFeatures: {
-        ...defaultSystemFeatures,
-        ...mockState.systemFeatures,
-      },
-    })
-  },
+  useSystemFeatures: () => ({
+    ...defaultSystemFeatures,
+    ...mockState.systemFeatures,
+  }),
 }))
 
 // Mock useInstalledPluginList hook