refactor: Tidy flake.nix and break it apart

outputs/homeConfigurations.nix

@@ -0,0 +1,26 @@
+{ ... }@inputs:
+
+let users = builtins.readDir ../users;
+    mkUser = username: _: {
+      imports = [
+        (import ../users/${username}/default.nix).homeConfiguration
+
+        inputs.self.homeManagerModules.default
+
+        inputs.sops-nix.homeManagerModules.sops
+        inputs.impermanence.homeManagerModules.impermanence
+
+        # Directory name should always match username.
+        ({ ... }: { home.username = username; })
+
+        ({ lib, ... }: {
+          nix = {
+            settings.experimental-features =
+              lib.mkDefault
+                [ "nix-command" "flakes" ];
+          };
+        })
+      ];
+    };
+in
+builtins.mapAttrs mkUser users