feat: Traktor NML export

[Radexito]

Adds the ability to export the library and playlists as a Traktor NML collection file, importable directly into Traktor Pro. Closes #28.

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Changes

src/audio/nmlWriter.js (new)

Pure-JS NML writer — no external dependencies.

• Generates valid Traktor Pro 3 NML (XML version 19)
• Encodes Traktor DIR paths in /:segment1/:segment2/: format
• Maps Camelot wheel keys to MUSICAL_KEY integer values (0–23) and key text
• Writes per-track COLLECTION entries containing:
  - LOCATION (volume + encoded directory + filename)
  - INFO (genre, key text, bitrate, playtime, rating, label, comment, import date)
  - TEMPO (BPM with 6 decimal places, supports bpm_override)
  - LOUDNESS (peak, perceived, and analyzed dB)
  - MUSICAL_KEY (numeric value for Traktor's key display)
  - CUE_V2 AutoGrid beat marker (uses intro_secs when available, defaults to 0 ms)
• Writes PLAYLISTS section with $ROOT folder node and named playlist child nodes, each containing PRIMARYKEY track references

src/main.js

• Added export-nml IPC handler — exports a single playlist plus all tracks to a chosen .nml file, emitting export-nml-progress events
• Added export-nml-all IPC handler — exports all tracks and all playlists

src/preload.js

• Exposed window.api.exportNml, window.api.exportNmlAll, and window.api.onExportNmlProgress

renderer/src/NmlExportModal.jsx + .css (new)

Export modal following the same idle → exporting → done/error pattern as the existing Rekordbox export modal. Lets the user pick an output folder via the directory dialog; writes to collection.nml.

renderer/src/Sidebar.jsx

Added two context menu items after the existing M3U export entries:

• Export playlist as NML…
• Export all as NML…

renderer/src/App.jsx

Wired NmlExportModal and the two new sidebar handler props.

src/tests/nmlWriter.test.js (new)

19 unit tests covering: file creation, XML structure, COLLECTION entry count, LOCATION encoding, TEMPO/BPM, MUSICAL_KEY mapping, INFO genre, LOUDNESS, CUE_V2 beat marker, PLAYLISTS section, PRIMARYKEY references, XML escaping, optional field
handling, and multi-track output. All passing.

vitest.config.js

Added nmlWriter.test.js to the unit test project.

package.json

Added "*.js" pattern to lint-staged so root-level JS files (e.g. vitest.config.js, eslint.config.js) are auto-formatted on commit.

.gitignore

Added *.so / .so. to prevent system shared libraries from being tracked.