fix: MP3 lyrics embedding via ID3v2.3 USLT frame

FFmpeg doesn't always embed lyrics correctly to MP3 files. This adds
manual ID3v2.3 USLT (Unsynchronized Lyrics) frame writing after FFmpeg
metadata embedding to ensure lyrics are properly stored.

Implementation:
- Extract lyrics from metadata (UNSYNCEDLYRICS or LYRICS key)
- Build ID3v2.3 compliant USLT frame with UTF-16LE encoding
- Insert or replace USLT frame in existing ID3v2.3 tag
- Create new ID3v2.3 tag if file has no ID3 header
- Skip gracefully for unsupported ID3 versions or flags

Also includes minor audio analysis improvements:
- Consistent dynamic range calculation (peak - rms)
- Filter out 'unknown' and 'n/a' labels
- Add -vn -sn -dn flags for more robust stream selection

lib/widgets/audio_analysis_widget.dart

@@ -455,8 +455,7 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
         final peakAmplitude =
             levelMetrics?.peakDb ?? spectrumResult.peakAmplitude;
         final rmsLevel = levelMetrics?.rmsDb ?? spectrumResult.rmsLevel;
-        final dynamicRange =
-            levelMetrics?.dynamicRangeDb ?? (peakAmplitude - rmsLevel);
+        final dynamicRange = peakAmplitude - rmsLevel;
         final spectralCutoffHz = spectrumResult.spectrum == null
             ? null
             : await compute(
@@ -601,7 +600,7 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
 
   String _formatCodecLabel(String codecName, String codecLongName) {
     final name = codecName.trim();
-    final longName = codecLongName.trim();
+    final longName = _normalizeAnalysisLabel(codecLongName);
     if (name.isEmpty) return longName;
     if (longName.isEmpty || longName.toLowerCase() == name.toLowerCase()) {
       return name.toUpperCase();
@@ -610,12 +609,19 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
   }
 
   String _formatContainerLabel(String formatName, String formatLongName) {
-    final longName = formatLongName.trim();
+    final longName = _normalizeAnalysisLabel(formatLongName);
     if (longName.isNotEmpty) return longName;
     final name = formatName.trim();
     return name.isEmpty ? '' : name.toUpperCase();
   }
 
+  String _normalizeAnalysisLabel(String value) {
+    final trimmed = value.trim();
+    final lower = trimmed.toLowerCase();
+    if (lower.isEmpty || lower == 'unknown' || lower == 'n/a') return '';
+    return trimmed;
+  }
+
   int _estimateTotalSamples({
     required Map<dynamic, dynamic> props,
     required double duration,
@@ -671,6 +677,9 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
         inputPath,
         '-map',
         '0:a:0',
+        '-vn',
+        '-sn',
+        '-dn',
         '-af',
         'astats=metadata=1:reset=0',
         '-f',
@@ -697,7 +706,6 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
       return _LevelMetrics(
         peakDb: peak,
         rmsDb: rms,
-        dynamicRangeDb: _parseLastAstatsValue(section, 'Dynamic range'),
         clippingSamples: clippingSamples,
         channelStats: channelStats,
       );
@@ -714,7 +722,12 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
         '-nostats',
         '-i',
         inputPath,
-        '-filter_complex',
+        '-map',
+        '0:a:0',
+        '-vn',
+        '-sn',
+        '-dn',
+        '-af',
         'ebur128=peak=true:framelog=quiet',
         '-f',
         'null',
@@ -757,12 +770,16 @@ class _AudioAnalysisCardState extends State<AudioAnalysisCard> {
       final channel = int.tryParse(match.group(1) ?? '') ?? 0;
       final section = match.group(2) ?? '';
       if (channel <= 0 || section.trim().isEmpty) continue;
+      final peakDb = _parseLastAstatsValue(section, 'Peak level dB');
+      final rmsDb = _parseLastAstatsValue(section, 'RMS level dB');
       stats.add(
         ChannelAnalysisStats(
           channel: channel,
-          peakDb: _parseLastAstatsValue(section, 'Peak level dB'),
-          rmsDb: _parseLastAstatsValue(section, 'RMS level dB'),
-          dynamicRangeDb: _parseLastAstatsValue(section, 'Dynamic range'),
+          peakDb: peakDb,
+          rmsDb: rmsDb,
+          dynamicRangeDb: peakDb != null && rmsDb != null
+              ? peakDb - rmsDb
+              : null,
           peakCount:
               _parseLastAstatsInt(section, 'Peak count') ??
               _parseLastAstatsInt(section, 'Peak count ch') ??
@@ -1021,14 +1038,12 @@ class _MediaInfo {
 class _LevelMetrics {
   final double peakDb;
   final double rmsDb;
-  final double? dynamicRangeDb;
   final int clippingSamples;
   final List<ChannelAnalysisStats> channelStats;
 
   const _LevelMetrics({
     required this.peakDb,
     required this.rmsDb,
-    this.dynamicRangeDb,
     this.clippingSamples = 0,
     this.channelStats = const [],
   });