local storage to make the calorie count persist. make count persist incase of tab closure

Hey Andrej, love how uncomplicated and practical this is. if you are open to it, i would like to suggest making it so the calorie data is persistant with the help of browser local storage. so that whatever calories we do add or subtract persist in case of closure of the tab. if its ok i would love to make a pr for this.

Start by locating the calorie count state and the add/subtract entry points in the app, then review how browser local storage can preserve that value. Done means the count survives closing and reopening the tab while additions and subtractions still work as before; no test file or filename is provided in the issue.

Written by the indexing model from the issue text.