Fix shell quoting for exec command arguments

Arguments with special characters (e.g. JSON strings) were passed
unquoted, causing breakage for commands like:
  --speculative-config '{"method":"qwen3_next_mtp","num_speculative_tokens":2}'

Use printf %q in launch-cluster.sh and shlex.quote() in run-recipe.py
to properly escape arguments.

launch-cluster.sh

@@ -115,7 +115,7 @@ while [[ "$#" -gt 0 ]]; do
             fi
             ACTION="exec"
             shift
-            COMMAND_TO_RUN="$@"
+            COMMAND_TO_RUN=$(printf "%q " "$@")
             break
             ;;
         *)