[mcp] Enable linger for drew

system/hosts/mcp/configuration.nix

@@ -64,6 +64,9 @@
       "docker-registry"
     ];
     shell = pkgs.zsh;
+    # Enable linger so that systemd services run for this user are started and
+    # persist even without an active session.
+    linger = true;
   };
 
   # List packages installed in system profile. To search, run: