steps 6-8: wire HybridStore into orchestrator, server, and main

- Add storage/hybrid.go: HybridStore composing PocketBase + MinIO backends
- Rewrite orchestrator to accept storage.Store instead of *writer.Writer
- Replace *writer.Writer with storage.Store in server.go and ui.go
- Wire audio cache, reading progress, chapter reads/writes through store
- Add rankingCacheAdapter in main.go to bridge context-free RankingPageCacher
  interface to HybridStore's context-aware methods

scraper/internal/orchestrator/orchestrator.go

@@ -19,7 +19,7 @@ import (
 	"sync"
 
 	"github.com/libnovel/scraper/internal/scraper"
-	"github.com/libnovel/scraper/internal/writer"
+	"github.com/libnovel/scraper/internal/storage"
 )
 
 // Config holds tunable parameters for the orchestrator.
@@ -28,7 +28,8 @@ type Config struct {
 	// Defaults to runtime.NumCPU() when 0.
 	Workers int
 
-	// StaticRoot is the path to the static/books output directory.
+	// StaticRoot is kept for backwards-compatibility but is no longer used
+	// when a Store is provided.
 	StaticRoot string
 
 	// SingleBookURL when non-empty causes the orchestrator to scrape only
@@ -40,13 +41,13 @@ type Config struct {
 type Orchestrator struct {
 	cfg     Config
 	novel   scraper.NovelScraper
-	writer  *writer.Writer
+	store   storage.Store
 	log     *slog.Logger
 	workers int
 }
 
-// New returns a new Orchestrator.
-func New(cfg Config, novel scraper.NovelScraper, log *slog.Logger) *Orchestrator {
+// New returns a new Orchestrator backed by the provided Store.
+func New(cfg Config, novel scraper.NovelScraper, log *slog.Logger, store storage.Store) *Orchestrator {
 	workers := cfg.Workers
 	if workers <= 0 {
 		workers = runtime.NumCPU()
@@ -54,7 +55,7 @@ func New(cfg Config, novel scraper.NovelScraper, log *slog.Logger) *Orchestrator
 	return &Orchestrator{
 		cfg:     cfg,
 		novel:   novel,
-		writer:  writer.New(cfg.StaticRoot),
+		store:   store,
 		log:     log,
 		workers: workers,
 	}
@@ -66,7 +67,6 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 	o.log.Info("orchestrator starting",
 		"source", o.novel.SourceName(),
 		"workers", o.workers,
-		"static_root", o.cfg.StaticRoot,
 	)
 
 	// chapterWork is the shared queue consumed by chapter worker goroutines.
@@ -89,8 +89,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 				default:
 				}
 
-				// Skip if already on disk.
-				if o.writer.ChapterExists(job.slug, job.ref) {
+				// Skip if already stored.
+				if o.store.ChapterExists(ctx, job.slug, job.ref) {
 					o.log.Debug("chapter already exists, skipping",
 						"book", job.slug, "chapter", job.ref.Number)
 					continue
@@ -107,7 +107,7 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 					continue
 				}
 
-				if err := o.writer.WriteChapter(job.slug, chapter); err != nil {
+				if err := o.store.WriteChapter(ctx, job.slug, chapter); err != nil {
 					o.log.Error("chapter write failed",
 						"book", job.slug,
 						"chapter", job.ref.Number,
@@ -135,8 +135,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 			return
 		}
 
-		// Persist / update metadata.yaml.
-		if err := o.writer.WriteMetadata(meta); err != nil {
+		// Persist / update metadata.
+		if err := o.store.WriteMetadata(ctx, meta); err != nil {
 			o.log.Error("metadata write failed", "slug", meta.Slug, "err", err)
 			// Continue — chapters can still be scraped.
 		}