Add torrent acquisition API client

[TheusHen]

Summary

This adds a typed acquisition API layer and a new Torrent & automation settings screen for the new torrent and automation endpoints.

It can register supported integrations, search releases through configured indexers, submit magnet/torrent releases to a selected download client, and trigger native commands in Readarr and other Arr applications. The new screen is available from Profile → Storage → Torrent & automation.

Implementation notes

• Added endpoint and release models, including magnet recognition.
• Added authenticated API calls for endpoint configuration, release search, release submission, and Arr commands.
• Added a small model test covering magnet releases.
• Added a route and settings entry point for managing torrent and automation integrations in the app.

Validation

• Formatted the new Dart files with dart format.

Flutter is not installed in this environment, so Flutter tests and full package analysis could not be run here.