Add activation script to clean up old NFS automount unit

default.nix

@@ -256,6 +256,16 @@ in
     # Enable NFS client support
     services.rpcbind.enable = true;
     
+    # Clean up old automount unit during activation
+    system.activationScripts.cleanupOldNfsAutomount = ''
+      if systemctl is-active mnt-nfs_share.automount &>/dev/null; then
+        systemctl stop mnt-nfs_share.automount || true
+      fi
+      if systemctl is-active mnt-nfs_share.mount &>/dev/null; then
+        systemctl stop mnt-nfs_share.mount || true
+      fi
+    '';
+    
     # NFS mount for shared storage
     fileSystems."/mnt/nfs_share" = {
       device = "192.168.1.249:/mnt/nfs_share";