Fix UDS path for FLET_SERVER_UDS_PATH environment variable

Updated the UDS path assignment to use the full path by joining appTempPath and the socket filename. This ensures the environment variable points to the correct socket location.

{{cookiecutter.out_dir}}/lib/main.dart

@@ -194,7 +194,7 @@ Future prepareApp() async {
     } else {
       // use UDS on other platforms
       pageUrl = "flet_$pid.sock";
-      environmentVariables["FLET_SERVER_UDS_PATH"] = pageUrl;
+      environmentVariables["FLET_SERVER_UDS_PATH"] = path.join(appTempPath, pageUrl);
     }
   }