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/bookfile/zip.go

@@ -26,6 +26,14 @@ func isImage(name string) bool {
 	return false
 }
 
+// junkEntry: macOS 打包混入的资源叉垃圾(__MACOSX/ 目录与 ._* AppleDouble),不是页
+func junkEntry(name string) bool {
+	if strings.HasPrefix(strings.ToLower(name), "__macosx/") {
+		return true
+	}
+	return strings.HasPrefix(path.Base(name), "._")
+}
+
 func PageIndex(f io.ReaderAt, size int64) ([]string, error) {
 	zr, err := zip.NewReader(f, size)
 	if err != nil {
@@ -36,6 +44,9 @@ func PageIndex(f io.ReaderAt, size int64) ([]string, error) {
 		if unsafeEntry(zf.Name) {
 			return nil, fmt.Errorf("%w: %s", ErrUnsafeZip, zf.Name)
 		}
+		if junkEntry(zf.Name) {
+			continue
+		}
 		if isImage(zf.Name) {
 			names = append(names, zf.Name)
 		}