chore: reworking nix module

[Mikilio]

Added a systemd service as it allows new configurations to apply on home-manager profile activation. Also added settings option allowing to configure any option using json. By convention because the config is modifiable by the program itself, I added it to XDG_DATA_HOME by default.

During debugging, I also fixed some minor issues on the side.

More PRs to come

• [x] All settings configurable via nix
• [ ] VPN settings
• [ ] Introducing settings to make non-essential features optional
• [ ] OSD
• [ ] make specific features optional (to tailor to minimalists or people that prefer other tools for specific use-cases)
• [ ] setup devenv with that allows for linting with minimal warnings or errors

Do you maintain a todo list of any kind? If so, it would be nice to make it public in some way, so I don't work on features you're already working on.

[Mikilio]

I see, thank you! Actually I had red warnings all over so I was wondering what environment you were using. Can I add a devenv for the project? Also: what about ai.proxyUrl? Do you want to avoid null in general?

[Mikilio]

The refactor is obviously opinionated, you insist I can make it more similar to your previous layout.