refactor(ranking): replace blob cache with per-item PocketBase storage

- Replace SetRanking/GetRanking/SetRankingPageHTML/GetRankingPageHTML blob methods
  with WriteRankingItem/ReadRankingItems/RankingFreshEnough per-item operations
- Add 24h staleness gate in ScrapeRanking to skip re-scraping fresh data
- Add GET /api/ranking endpoint returning []RankingItem sorted by rank
- Remove RankingPageCacher interface and rankingCacheAdapter adapter
- Update integration tests to use new per-item upsert semantics
- Include e2e test suite (scraper/internal/e2e/)

scraper/cmd/scraper/main.go

@@ -119,7 +119,7 @@ func run(log *slog.Logger) error {
 		return fmt.Errorf("storage init failed: %w", err)
 	}
 
-	nf := novelfire.New(bc, log, urlClient, &rankingCacheAdapter{store: store})
+	nf := novelfire.New(bc, log, urlClient, store)
 
 	workers := 0
 	if s := os.Getenv("SCRAPER_WORKERS"); s != "" {
@@ -215,20 +215,6 @@ func envOr(key, fallback string) string {
 	return fallback
 }
 
-// rankingCacheAdapter bridges storage.HybridStore (context-aware) to the
-// context-free scraper.RankingPageCacher interface expected by novelfire.New.
-type rankingCacheAdapter struct {
-	store *storage.HybridStore
-}
-
-func (a *rankingCacheAdapter) WriteRankingPageCache(page int, html string) error {
-	return a.store.WriteRankingPageCache(context.Background(), page, html)
-}
-
-func (a *rankingCacheAdapter) ReadRankingPageCache(page int) (string, error) {
-	return a.store.ReadRankingPageCache(context.Background(), page)
-}
-
 func printUsage() {
 	fmt.Fprintf(os.Stderr, `libnovel scraper