Feature: Spotify integration for library synchronization and music playback

[cuevasrja]

Is your feature request related to a problem? Please describe.
Currently, listening to music through the application relies on local files or non-centralized external sources. As a regular Spotify user, I'm always frustrated when I have to constantly switch between Lotus and the official Spotify app to manage my library and playback. It interrupts the seamless and unified experience that Lotus provides.

Describe the solution you'd like
I would like a native integration with Spotify accounts that includes:

1. Secure authentication: Option to log in with a Spotify account (via OAuth).
2. Library synchronization: Ability to view and interact with my playlists, saved albums, and "Liked Songs" directly within the Lotus interface.
3. Integrated playback: Full playback controls (play, pause, skip track, volume, and song progress bar) embedded within Lotus.

Describe alternatives you've considered

• Remote control (Spotify Connect): Using the Spotify API solely to control playback on the official Spotify app running in the background, rather than streaming audio directly through Lotus.
• Using both apps simultaneously: Continuing to use the native Spotify app separately, although this breaks the workflow within Lotus.

Additional context

• This feature could be implemented using the Spotify Web API and the Spotify Web Playback SDK (keeping in mind that direct playback typically requires a Spotify Premium account).
• To avoid global rate limits, an option could be added in the settings allowing users to provide their own API keys (Client ID / Client Secret).