v3.2.0

refactor: extract shared modules, add checkbox UI, dedup, YouTube docs

- Extract gui_utils.py (shared emit) and search_strategies.py (shared search logic)
- Remove 3x duplicated emit() and 2x duplicated search functions
- Add trackId to match emissions for GUI playlist selection
- Add checkbox-based track selection: select/deselect which songs to add
- Add 'Add Selected to Playlist' toolbar with Select All toggle
- Add 'addtracks' CLI command for GUI selective playlist addition
- Deduplicate tracks by Spotify ID and by display name
- Fix progress bar: emit total count before scanning
- Fix stats double-counting in app.js (progress vs match/no_match)
- In GUI mode, don't auto-add to playlist (user selects via checkboxes)
- Fix cli.py arg order: username before --gui for argparse compatibility
- Combine 17 YouTube noise regexes into single compiled pattern
- Deduplicate YouTube playlist entries by title
- Update PyInstaller spec with new hidden imports
- Align version to 3.2.0 across package.json and pyproject.toml
- Add yt-dlp to pyproject.toml dependencies
- Update README: YouTube CLI docs, checkbox feature, audio formats, build guide
- Update Korean README section with YouTube and checkbox docs