[CLEAN] Synthetic Benchmark PR #30102 - fix(web): remove incorrect placeholderData usage in useExploreAppList

[ofir-frd]

Benchmark PR langgenius#30102

Type: Clean (correct implementation)

Original PR Title: fix(web): remove incorrect placeholderData usage in useExploreAppList
Original PR Description: ## Summary

Fixes incorrect placeholderData usage in useExploreAppList that was introduced in PR langgenius#30076.

Background

PR langgenius#30076 migrated the Explore app list from useSWR to TanStack Query, but used placeholderData: exploreAppListInitialData (empty arrays) to simulate the loading state. This is an anti-pattern according to TanStack Query's official documentation.

Problem

According to TanStack Query docs:

placeholderData: Provides temporary data to display while a query is in the pending state. Unlike initialData, placeholder data is NOT persisted to the cache. It should be used for meaningful temporary content (e.g., skeleton data, previous results), NOT empty arrays to mock loading.

The previous implementation had these issues:

1. Broke Query state machine: With placeholderData, data is never undefined, so isLoading is always false
2. Unable to distinguish states: Cannot tell the difference between "loading" and "truly empty data"
3. Semantic mismatch: Empty arrays are not "temporary data" - they're just absence of data

Solution

Remove placeholderData and use the proper isLoading state to control loading:

Before:

const {
  data: { categories, allList } = exploreAppListInitialData,
} = useExploreAppList()

if (!categories || categories.length === 0) {
  return <Loading />  // Shows loading even when truly empty
}

After:

const {
  data,
  isLoading,
} = useExploreAppList()

if (isLoading) {
  return <Loading />  // Only shows during initial fetch
}

if (!data || data.categories.length === 0) {
  return <EmptyState />  // Shows when actually empty
}

Changes

• web/service/use-explore.ts: Remove exploreAppListInitialData export and placeholderData option
• web/app/components/explore/app-list/index.tsx: Use isLoading for loading state, remove unused PageType enum
• web/app/components/app/create-app-dialog/app-list/index.tsx: Use isLoading for loading state

Testing

• pnpm lint:fix - Passes
• pnpm type-check:tsgo - Passes

References

• TanStack Query official docs on placeholderData
• TanStack Query official docs on initialData vs placeholderData
  Original PR URL: fix(web): remove incorrect placeholderData usage in useExploreAppList langgenius/dify#30102