## Goal The dataset is American: ingredients use cups, ounces, pounds and inches, and directions use °F. Add a toggle so users can switch between US and metric (EU) units. Conversion happens **only in the frontend** at display time; the database keeps the original text. ## Acceptance criteria - [ ] Toggle US / Metric visible in the recipe view (or header), keyboard accessible and labelled - [ ] Choice remembered across page loads and applied everywhere quantities are shown - [ ] Pure conversion function, e.g. `convertIngredient(text, 'metric')`: - cups → ml/dl, fl oz → ml, oz → g, lb → g/kg, inches → cm, °F → °C (also inside directions) - handles fractions and mixed numbers (`1 1/2`, `½`, `2¾`) and ranges (`3½–4-lb.`) - leaves text it doesn't recognise unchanged - rounds to sensible kitchen values (e.g. 236.6 ml → 240 ml) - [ ] Vitest unit tests for the converter with real examples from the dataset ## Notes tsp/tbsp can stay as they are (also used in metric recipes); converting them to ml is optional.