Pass around `perSystem`'s `pkgs` instances to the system configurations
Some more refactoring in `configurations`' `mkHost` functions
Also start using `home-manager`'s `useGlobalPkgs` option
Also use `mkShellNoCC` for default `devShell`
Also `nix flake update`
Add `nixpkgs-cross-overlay` to substituters
Add `google-cloud-sdk` to `home.packages`
Remove comment (from old experiments) from `reo101-shell` HM module
Remove `pinentry-touchid` from `brew` packages (causing issues, no longer used)