refactor: Move user config into modules/

modules/home/users/crumb/age.nix

@@ -0,0 +1,25 @@
+{ config, lib, pkgs, ... }:
+
+let
+  mutableSymlink = config.lib.file.mkOutOfStoreSymlink;
+  cfg = config.sydnix.users.crumb.age;
+in
+{
+  options.sydnix.users.crumb.age.enable = lib.mkEnableOption "Age, à la crumb";
+
+  config = lib.mkIf cfg.enable {
+    home.packages = [
+      # Rage supports pinentry while Age does not.
+      pkgs.rage
+    ];
+
+    # We use a mutable symlink to avoid placing the key inside the
+    # world-readable store.
+    home.file."private-keys/age/${config.home.username}.age".source =
+      mutableSymlink "/persist/private-keys/age/${config.home.username}.age";
+
+    home.file."public-keys/age/${config.home.username}.pub".source =
+      ../../../../public-keys/age/${config.home.username}.pub;
+  };
+}
+