feat: resolve audio metadata from file, backfill placeholder quality labels with actual bit depth and sample rate

lib/utils/string_utils.dart

@@ -5,3 +5,47 @@ String? normalizeOptionalString(String? value) {
   if (trimmed.toLowerCase() == 'null') return null;
   return trimmed;
 }
+
+String formatSampleRateKHz(int sampleRate) {
+  final khz = sampleRate / 1000;
+  final precision = sampleRate % 1000 == 0 ? 0 : 1;
+  return '${khz.toStringAsFixed(precision)}kHz';
+}
+
+String? buildDisplayAudioQuality({
+  int? bitDepth,
+  int? sampleRate,
+  int? bitrateKbps,
+  String? format,
+  String? storedQuality,
+}) {
+  if (bitrateKbps != null && bitrateKbps > 0) {
+    final normalizedFormat = normalizeOptionalString(format)?.toUpperCase();
+    return normalizedFormat != null
+        ? '$normalizedFormat ${bitrateKbps}kbps'
+        : '${bitrateKbps}kbps';
+  }
+
+  if (bitDepth != null &&
+      bitDepth > 0 &&
+      sampleRate != null &&
+      sampleRate > 0) {
+    return '$bitDepth-bit/${formatSampleRateKHz(sampleRate)}';
+  }
+
+  return normalizeOptionalString(storedQuality);
+}
+
+bool isPlaceholderQualityLabel(String? quality) {
+  final normalized = normalizeOptionalString(quality)?.toLowerCase();
+  if (normalized == null) return false;
+
+  return const {
+    'best',
+    'lossless',
+    'hi-res',
+    'hi-res-max',
+    'high',
+    'cd',
+  }.contains(normalized);
+}