00af97e3

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Add nix flake with web app package and devShell

- Default package builds the React/Vite web app using buildNpmPackage
- Default devShell provides Node.js 22
- Both exposed as checks so nix flake check builds everything
- Uses nixos-25.11 nixpkgs, x86_64-linux only