Fix nixos-rebuild agent execution: run as cm user

Change sudo command to use '-u cm' to run nixos-rebuild as the cm user
instead of root, allowing access to /home/cm/nixosbox directory.

agent/src/agent.rs

@@ -293,8 +293,10 @@ impl Agent {
             info!("Maintenance mode enabled");
         }
 
-        // Change to nixos directory and execute rebuild
+        // Change to nixos directory and execute rebuild as cm user
         let output = tokio::process::Command::new("sudo")
+            .arg("-u")
+            .arg("cm")
             .arg("nixos-rebuild")
             .arg("switch")
             .current_dir(nixos_path)