refactor(flake): move nvim config to a package

Add it as a package instead of symlinking it into the `~/.config.nvim`
directory.

flake.nix

@@ -12,7 +12,12 @@
       systems = [ "x86_64-linux" ];
 
       perSystem = { pkgs, self', nixpkgs, ... }: {
-        packages.default = self'.packages.activate;
+        packages = {
+          opdavies-nvim = pkgs.vimUtils.buildVimPlugin {
+            name = "opdavies-nvim";
+            src = ./config/neovim;
+          };
+        };
 
         formatter = pkgs.nixpkgs-fmt;
       };

home-manager/modules/common.nix

@@ -203,6 +203,8 @@ in
 
       # Themes
       vimPlugins.catppuccin-nvim
+
+      inputs.self.packages.${pkgs.system}.opdavies-nvim
     ];
 
     extraPackages = with pkgs; [
@@ -254,11 +256,6 @@ in
     recursive = true;
   };
 
-  xdg.configFile.nvim = {
-    source = ../../config/neovim;
-    recursive = true;
-  };
-
   xdg.configFile.phpactor = {
     source = ../../config/phpactor;
     recursive = true;