Node.js recipe scaling and shopping list tool

Build a self-contained Node.js command-line application for scaling recipes and consolidating a shopping list. Use one documented JSON input file containing recipes with id, name, original servings, and ingredients (name, numeric quantity, unit), plus a plan listing each selected recipe id and desired servings. The CLI reads that file, scales quantities by desired/original servings, combines entries only when normalized ingredient name and unit match, sorts output deterministically, and prints a JSON shopping list. Refuse malformed JSON, unknown recipe ids, non-positive servings or quantities, and unsupported units with actionable errors. Include a small example input, README usage, and automated tests for scaling, consolidation, unit separation, and invalid inputs. Use only local files and no external service or API. Do not modify mgtf/atoma.

Continue the existing recipe scaling and shopping list tool from its delivered workspace. Do not change the tool's behaviour. Write a user guide as docs/USER-GUIDE.md that explains, from the actual source and the existing README, the JSON input format with one complete annotated example, every command and option the tool accepts with its exact output for the bundled example data, how quantities are rounded and units consolidated, and the error messages a person can meet and what to do about each. Every command and output in the guide must be verified against the real tool before being written down, and the README gains a short link to the guide. Completion is observable by following the guide from a clean checkout and seeing the documented outputs.