feat!(flake): update homix

Update flake (`neovim-nightly-overlay` is fixed)
Format all `.nix` files
Unify package/module argument order:
    - `inputs`, `outputs`, `lib`, `pkgs`, `config`, ...
Move Jellyfin config to a `NixOS` module (first one, yay)
Add `direnv` to `reo101-shell` modules (was used, but not defined as wanted)
    - TODO: make it optional (module config options)

modules/nixos/default.nix

@@ -4,4 +4,5 @@
 {
   # List your module files here
   # my-module = import ./my-module.nix;
+  jellyfin = import ./jellyfin.nix;
 }