Canonicalizes track identifier tags and validates embedded cover headers once at internal/audiotag entry, branched directly off upstream/v1:
internal/util: Foldsbarcode.gointoidentifier.go(NormalizeUUID,NormalizeISRC,NormalizeGTIN,CalculateCheckDigitwithNormalizeGTINlogic unchanged fromupstream/v1), renamesformatutil.go->format.goandhttputil.go->http.go, and addsExtractYear.internal/audiotag: CanonicalizesMBRecordingID,MBReleaseID,MBReleaseGroupID,ISRC,Year, andFilePathonce inReadTrack, renames*Exthelpers toIsAudioExtension/IsBrowserStreamableExtension/IsCoverExtension, and adds header-only JPEG/PNGValidateCoverinReadCover.