feat: ranking page pagination, popular URL, and per-page HTML disk cache

- Switch ScrapeRanking to novelfire.net/genre-all/sort-popular URL and updated DOM selectors (div.novel-item, h3.novel-title, div.genres)
- Replace 5 hardcoded refresh buttons with dynamic 100-page paginator (smart ellipsis via rankingPageNums)
- Add RankingPageCacher interface and writer methods to cache raw HTML per page under static/books/_ranking_cache/page-N.html
- ScrapeRanking serves from disk cache on hit and writes to cache on miss, skipping Browserless round-trip
- Thread writer as PageCacher through novelfire.New and main.go
- Add TestScrapeRanking_CacheHit and TestScrapeRanking_CacheMiss tests

scraper/cmd/scraper/main.go

@@ -88,7 +88,9 @@ func run(log *slog.Logger) error {
 	bc := newBrowserClient(strategy, browserCfg)
 	urlClient := newBrowserClient(urlStrategy, browserCfg)
 
-	nf := novelfire.New(bc, log, urlClient)
+	staticRoot := envOr("SCRAPER_STATIC_ROOT", "./static/books")
+	w := writer.New(staticRoot)
+	nf := novelfire.New(bc, log, urlClient, w)
 
 	workers := 0
 	if s := os.Getenv("SCRAPER_WORKERS"); s != "" {
@@ -103,7 +105,7 @@ func run(log *slog.Logger) error {
 
 	oCfg := orchestrator.Config{
 		Workers:    workers,
-		StaticRoot: envOr("SCRAPER_STATIC_ROOT", "./static/books"),
+		StaticRoot: staticRoot,
 	}
 
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)