feat(tidal): convert M4A to MP3/Opus for HIGH quality, remove LOSSY option

- Add tidalHighFormat setting (mp3_320 or opus_128) for Tidal HIGH quality
- Add convertM4aToLossy() in FFmpegService for M4A to MP3/Opus conversion
- Remove inefficient LOSSY option (FLAC download then convert)
- Update download_queue_provider to handle HIGH quality conversion
- Clean up LOSSY references from download_service_picker and log messages
- Update Go backend: amazon.go, tidal.go, metadata.go improvements
- UI: minor updates to album, playlist, and home screens

go_backend/amazon.go

@@ -299,8 +299,13 @@ func downloadFromAmazon(req DownloadRequest) (AmazonDownloadResult, error) {
 	existingMeta, metaErr := ReadMetadata(outputPath)
 	actualTrackNum := req.TrackNumber
 	actualDiscNum := req.DiscNumber
+	actualDate := req.ReleaseDate
+	actualAlbum := req.AlbumName
+	actualTitle := req.TrackName
+	actualArtist := req.ArtistName
 
 	if metaErr == nil && existingMeta != nil {
+		// Use track/disc number from Amazon file if request has default values
 		if existingMeta.TrackNumber > 0 && (req.TrackNumber == 0 || req.TrackNumber == 1) {
 			actualTrackNum = existingMeta.TrackNumber
 			GoLog("[Amazon] Using track number from file: %d (request had: %d)\n", actualTrackNum, req.TrackNumber)
@@ -309,15 +314,29 @@ func downloadFromAmazon(req DownloadRequest) (AmazonDownloadResult, error) {
 			actualDiscNum = existingMeta.DiscNumber
 			GoLog("[Amazon] Using disc number from file: %d (request had: %d)\n", actualDiscNum, req.DiscNumber)
 		}
+		// Use release date from Amazon file if request doesn't have it
+		if existingMeta.Date != "" && req.ReleaseDate == "" {
+			actualDate = existingMeta.Date
+			GoLog("[Amazon] Using release date from file: %s\n", actualDate)
+		}
+		// Use album from Amazon file if request doesn't have it
+		if existingMeta.Album != "" && req.AlbumName == "" {
+			actualAlbum = existingMeta.Album
+			GoLog("[Amazon] Using album from file: %s\n", actualAlbum)
+		}
+		// Log existing metadata for debugging
+		GoLog("[Amazon] Existing metadata - Title: %s, Artist: %s, Album: %s, Date: %s\n",
+			existingMeta.Title, existingMeta.Artist, existingMeta.Album, existingMeta.Date)
 	}
 
-	// Embed metadata using Spotify data
+	// Embed metadata using Spotify/Deezer data (preferred for consistency)
+	// but use Amazon file data as fallback for missing fields
 	metadata := Metadata{
-		Title:       req.TrackName,
-		Artist:      req.ArtistName,
-		Album:       req.AlbumName,
+		Title:       actualTitle,
+		Artist:      actualArtist,
+		Album:       actualAlbum,
 		AlbumArtist: req.AlbumArtist,
-		Date:        req.ReleaseDate,
+		Date:        actualDate,
 		TrackNumber: actualTrackNum,
 		TotalTracks: req.TotalTracks,
 		DiscNumber:  actualDiscNum,
@@ -327,11 +346,20 @@ func downloadFromAmazon(req DownloadRequest) (AmazonDownloadResult, error) {
 		Copyright:   req.Copyright,
 	}
 
-	// Use cover data from parallel fetch
+	// Use cover data from parallel fetch, or extract from Amazon file if not available
 	var coverData []byte
-	if parallelResult != nil && parallelResult.CoverData != nil {
+	if parallelResult != nil && parallelResult.CoverData != nil && len(parallelResult.CoverData) > 0 {
 		coverData = parallelResult.CoverData
 		GoLog("[Amazon] Using parallel-fetched cover (%d bytes)\n", len(coverData))
+	} else {
+		// Try to extract existing cover from Amazon file
+		existingCover, coverErr := ExtractCoverArt(outputPath)
+		if coverErr == nil && len(existingCover) > 0 {
+			coverData = existingCover
+			GoLog("[Amazon] Using existing cover from Amazon file (%d bytes)\n", len(coverData))
+		} else {
+			GoLog("[Amazon] No cover available (parallel fetch failed and no existing cover)\n")
+		}
 	}
 
 	if err := EmbedMetadataWithCoverData(outputPath, metadata, coverData); err != nil {