feat(cbz): adapt reader to real archive structure — PageIndex skips macOS junk (__MACOSX/ and ._ AppleDouble were polluting pages with 163-byte blacks), pages endpoint derives chapters[{title,start}] from folder layout, imageless zip now lands state=error instead of an empty reader, CbzReader gains 目录 sidebar + prev/next chapter (TextReader pattern, rd-* classes); pagesidx cache key bumped for one-time invalidation; e2e on 311MB 調教開關：第二季.zip: 15048→7524 real pages, 52 chapters, all JPEGs

backend/internal/scanner/scanner.go

@@ -2,6 +2,7 @@ package scanner
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"io/fs"
@@ -146,6 +147,9 @@ func (s *Scanner) add(ctx context.Context, libID int64, root, rel string, ds dis
 		idx, err := s.zipIndex(root, rel)
 		pageCount = len(idx)
 		idxErr = err
+		if idxErr == nil && pageCount == 0 { // 视频/文档 zip 不是漫画,空白 reader 没有意义
+			idxErr = errors.New("no images in archive")
+		}
 	}
 	id, err := s.st.InsertBook(ctx, libID, rel, titleOf(rel), format, ds.size, ds.modTS, pageCount)
 	if err != nil {
@@ -167,6 +171,9 @@ func (s *Scanner) update(ctx context.Context, libID, bookID int64, root, rel str
 		idx, err := s.zipIndex(root, rel)
 		pageCount = len(idx)
 		idxErr = err
+		if idxErr == nil && pageCount == 0 { // 视频/文档 zip 不是漫画,空白 reader 没有意义
+			idxErr = errors.New("no images in archive")
+		}
 	}
 	if err := s.st.UpdateBookFile(ctx, bookID, ds.size, ds.modTS, pageCount); err != nil {
 		log.Printf("scan: update %s: %v", rel, err)