feat(copyparty): set library unix permissions

Without these, Kavita cannot access files in the library properly

packetmix/systems/teal/copyparty.nix

···
                 "minion"
               ];
             };
+
+            flags = {
+              chmod_f = "770";
+              chmod_d = "770";
+              gid = "974";
+            };
           };
         };
       };