feat: v3.1.2 - MP3 option, dominant color headers, sticky titles, disc separation

Added:
- MP3 quality option with FLAC-to-MP3 conversion (320kbps)
- Dominant color header backgrounds on detail screens
- Spotify-style sticky title on scroll (album, playlist, artist screens)
- Disc separation for multi-disc albums
- Album grouping in recent downloads
- 50% screen width cover art

Changed:
- Improved FFmpeg FLAC-to-MP3 conversion workflow
- AppBar uses theme surface color when collapsed

Fixed:
- Empty catch blocks with proper comments
- Russian plural forms (ICU syntax)

Dependencies:
- Added palette_generator ^0.3.3+4

pubspec.lock

@@ -653,6 +653,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.2.0"
+  palette_generator:
+    dependency: "direct main"
+    description:
+      name: palette_generator
+      sha256: "4420f7ccc3f0a4a906144e73f8b6267cd940b64f57a7262e95cb8cec3a8ae0ed"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.3.3+7"
   path:
     dependency: transitive
     description: