change copyparty folders and add write access

hosts/sin/secrets.nix

@@ -10,5 +10,9 @@
       file = ./secrets/airvpn_wireguard_key_env.age;
       mode = "700";
     };
+    copyparty-serhao = {
+      file = ./secrets/copyparty-serhao.age;
+      mode = "700";
+    };
   };
 }