Added FLAC files metadata using mutagen package.

[marco-boundi]

feat(audio): Add comprehensive FLAC metadata support

Implement robust FLAC metadata handling using mutagen library to enhance audio file information. This change enables proper tagging of FLAC files with complete song metadata.

Key improvements:

• Add basic track metadata (title, artist, album)
• Support album artist tag distinction
• Include release year from physical release date
• Add disc and track numbering
• Support genre and composer tags
• Implement album cover art embedding
• Handle total tracks count from album data

The implementation gracefully handles missing metadata fields and provides error reporting for failed operations.

Technical details:

• Uses mutagen.FLAC for metadata manipulation
• Implements Picture class for cover art embedding
• Maintains backwards compatibility with existing MP3 metadata
• Adds proper error handling for all metadata operations