feat(anki): add enable option

modules/anki/default.nix

@@ -1,6 +1,15 @@
+{ lib, config, ... }:
+
+let
+  cfg = config.anki;
+in
 {
-  config.secrets.groups.anki = [
-    "sync-user"
-    "sync-key"
-  ];
+  options.anki.enable = lib.mkEnableOption "anki";
+
+  config = lib.mkIf cfg.enable {
+    secrets.groups.anki = [
+      "sync-user"
+      "sync-key"
+    ];
+  };
 }