Improve token flow reliability, metadata fallback tagging, and proxy-aware networking

[Laynholt]

Summary

This PR combines the latest reliability and metadata improvements across token fetching, batch downloads, tagging, and networking.

What changed

• Added a Windows browser fallback for token extraction:

  • Uses Microsoft Edge when Google Chrome is not available.
  • Closes the temporary browser window immediately after token retrieval.

• Fixed first-run batch download behavior when no token exists:

  • Batch downloads now automatically fetch and refresh the session token instead of failing all tracks.

• Improved metadata tagging for downloaded tracks:

  • Genre resolution now uses a multi-source fallback chain: MusicBrainz -> Chosic -> Deezer (if previous sources are empty or unavailable).
  • Release year is now correctly parsed and embedded into track metadata tags.
  • Fixed playlist track numbering in embedded tags: track number is now resolved from album metadata (via track ID) instead of defaulting to 1.

• Added proxy-aware HTTP behavior for backend requests:

  • Introduced a shared HTTP client/transport across backend network calls.
  • Uses standard proxy environment variables (HTTP_PROXY, HTTPS_PROXY, NO_PROXY).
  • On Windows, falls back to system proxy settings (Internet Settings) when environment variables are not set.