️🛠 - Add track comments field

[maxwellmattryan]

Description

DJs heavily use comments for set notes, mix notes, and custom categorization. Rekordbox has two comment fields; Crate has none. This adds a comments field to tracks across the full stack.

Scope:

• DB migration: add comment TEXT column to tracks table
• Update Rust Track model and TypeScript Track type
• Metadata extraction: read Comment tag from audio files on import (ID3 COMM, Vorbis COMMENT)
• UI: comment column in track list, editable field in track editor, bulk edit support
• Export: map to PDB/Device Library Plus comment field
• Rekordbox sync (🛠 - Add library syncing with Rekordbox #39): map to djmdContent comment field
• Smart playlist support: add "Comment" as a text condition field

Open questions

• Should we support both Comment and Comment2 fields like Rekordbox, or just one?
• Should comments be written back to audio file tags on edit, or only stored in Crate's database?

Acceptance criteria

• Tracks have a comment field visible in the track list and editable in the track editor
• Comments are extracted from audio file metadata on import (ID3 COMM, Vorbis COMMENT)
• Comments can be bulk-edited across multiple selected tracks
• Comments are included in USB export (PDB/Device Library Plus)
• Comments are available as a text condition in smart playlists

Tasks

TBD