feat: add PDF/EPUB import functionality

- Add ImportTask/ImportResult types to domain.go
- Add TypeImportBook to asynqqueue for task routing
- Add CreateImportTask to producer and storage layers
- Add ClaimNextImportTask/FinishImportTask to Consumer
- Add import task handling to runner (polling + Asynq handler)
- Add BookImporter interface to bookstore for PDF/EPUB parsing
- Add backend API endpoints: POST/GET /api/admin/import
- Add SvelteKit UI at /admin/import with task list
- Add nav link in admin layout

Note: PDF/EPUB parsing is a placeholder - needs external library integration.

backend/internal/asynqqueue/producer.go

@@ -87,6 +87,29 @@ func (p *Producer) CreateTranslationTask(ctx context.Context, slug string, chapt
 	return p.pb.CreateTranslationTask(ctx, slug, chapter, lang)
 }
 
+// CreateImportTask creates a PocketBase record then enqueues an Asynq job for PDF/EPUB import.
+func (p *Producer) CreateImportTask(ctx context.Context, slug, title, fileType, objectKey string) (string, error) {
+	id, err := p.pb.CreateImportTask(ctx, slug, title, fileType, objectKey)
+	if err != nil {
+		return "", err
+	}
+
+	payload := ImportPayload{
+		PBTaskID:  id,
+		Slug:      slug,
+		Title:     title,
+		FileType:  fileType,
+		ObjectKey: objectKey,
+	}
+	if err := p.enqueue(ctx, TypeImportBook, payload); err != nil {
+		// Non-fatal: PB record exists; runner will pick it up on next poll.
+		p.log.Warn("asynq enqueue import failed (task still in PB, runner will poll)",
+			"task_id", id, "err", err)
+		return id, nil
+	}
+	return id, nil
+}
+
 // CancelTask delegates to PocketBase; Asynq jobs may already be running and
 // cannot be reliably cancelled, so we only update the audit record.
 func (p *Producer) CancelTask(ctx context.Context, id string) error {

backend/internal/asynqqueue/tasks.go

@@ -23,6 +23,7 @@ const (
 	TypeAudioGenerate   = "audio:generate"
 	TypeScrapeBook      = "scrape:book"
 	TypeScrapeCatalogue = "scrape:catalogue"
+	TypeImportBook      = "import:book"
 )
 
 // AudioPayload is the Asynq job payload for audio generation tasks.
@@ -44,3 +45,12 @@ type ScrapePayload struct {
 	FromChapter int    `json:"from_chapter"` // 0 unless Kind=="book_range"
 	ToChapter   int    `json:"to_chapter"`   // 0 unless Kind=="book_range"
 }
+
+// ImportPayload is the Asynq job payload for PDF/EPUB import tasks.
+type ImportPayload struct {
+	PBTaskID  string `json:"pb_task_id"`
+	Slug      string `json:"slug"`
+	Title     string `json:"title"`
+	FileType  string `json:"file_type"` // "pdf" or "epub"
+	ObjectKey string `json:"object_key"` // MinIO path to uploaded file
+}