Add Hi-Res authenticity check

Introduce a per-file Hi-Res authenticity checker and optional auto re-download for flagged fake Hi-Res downloads. Adds Rust checker modules (fft, evidence, FLAC/WAV decoding, tests) and a mobile API (check_hires_authenticity). Wire platform bindings for Android/iOS and PlatformBridge. Add Dart HiResCheckService, UI HiResCheckCard, settings toggle (redownloadFakeHiRes) and integration in the download pipeline to quarantine and replace suspicious files with LOSSLESS when safe. Adds claxon FLAC dependency.

lib/models/settings.dart

@@ -77,6 +77,8 @@ class AppSettings {
   final String locale;
   final String lyricsMode;
   final bool autoConvertDownloads;
+  // Re-download a Hi-Res request at LOSSLESS when the file measures as fake.
+  final bool redownloadFakeHiRes;
   final String autoConvertFormat; // 'mp3', 'aac' (M4A), or 'opus'
   final String autoConvertBitrate; // '128k', '192k', '256k', or '320k'
   final bool
@@ -172,6 +174,7 @@ class AppSettings {
     this.locale = 'system',
     this.lyricsMode = 'embed',
     this.autoConvertDownloads = false,
+    this.redownloadFakeHiRes = false,
     this.autoConvertFormat = 'mp3',
     this.autoConvertBitrate = '320k',
     this.useAllFilesAccess = false,
@@ -260,6 +263,7 @@ class AppSettings {
     String? locale,
     String? lyricsMode,
     bool? autoConvertDownloads,
+    bool? redownloadFakeHiRes,
     String? autoConvertFormat,
     String? autoConvertBitrate,
     bool? useAllFilesAccess,
@@ -353,6 +357,7 @@ class AppSettings {
       locale: locale ?? this.locale,
       lyricsMode: lyricsMode ?? this.lyricsMode,
       autoConvertDownloads: autoConvertDownloads ?? this.autoConvertDownloads,
+      redownloadFakeHiRes: redownloadFakeHiRes ?? this.redownloadFakeHiRes,
       autoConvertFormat: autoConvertFormat ?? this.autoConvertFormat,
       autoConvertBitrate: autoConvertBitrate ?? this.autoConvertBitrate,
       useAllFilesAccess: useAllFilesAccess ?? this.useAllFilesAccess,

lib/models/settings.g.dart

@@ -63,6 +63,7 @@ AppSettings _$AppSettingsFromJson(Map<String, dynamic> json) => AppSettings(
   locale: json['locale'] as String? ?? 'system',
   lyricsMode: json['lyricsMode'] as String? ?? 'embed',
   autoConvertDownloads: json['autoConvertDownloads'] as bool? ?? false,
+  redownloadFakeHiRes: json['redownloadFakeHiRes'] as bool? ?? false,
   autoConvertFormat: json['autoConvertFormat'] as String? ?? 'mp3',
   autoConvertBitrate: json['autoConvertBitrate'] as String? ?? '320k',
   useAllFilesAccess: json['useAllFilesAccess'] as bool? ?? false,
@@ -152,6 +153,7 @@ Map<String, dynamic> _$AppSettingsToJson(
   'locale': instance.locale,
   'lyricsMode': instance.lyricsMode,
   'autoConvertDownloads': instance.autoConvertDownloads,
+  'redownloadFakeHiRes': instance.redownloadFakeHiRes,
   'autoConvertFormat': instance.autoConvertFormat,
   'autoConvertBitrate': instance.autoConvertBitrate,
   'useAllFilesAccess': instance.useAllFilesAccess,