sync: merge s0.sermc.net LXC configuration

- Add users.luochen570 user config
- Add nix substituters (Tsinghua mirror)
- Add nix experimental-features (nix-command, flakes)
- Set system.stateVersion to 25.05

hosts/nixos-lxc/configuration.nix

@@ -30,6 +30,12 @@
     };
   };
 
+  # 用户账户配置
+  users.users.luochen570 = {
+    isNormalUser = true;
+    extraGroups = [ "wheel" "networkmanager" ];
+  };
+
   security.sudo.wheelNeedsPassword = false;
 
   services.resolved = {
@@ -39,4 +45,8 @@
     '';
   };
 
+  nix.settings.substituters = [ "https://mirrors.tuna.tsinghua.edu.cn/nix-channels/store" ];
+  nix.settings.experimental-features = [ "nix-command" "flakes" ];
+
+  system.stateVersion = "25.05";
 }