Feature: Add alcohol flag to quick-add command

[milldr]

Summary

Add an -a / --alcohol flag to crono quick-add to track alcohol grams alongside other macronutrients.

Background

Alcohol contains 7 calories per gram and is metabolized differently than other macros. For accurate tracking (especially on big nights 🍷), it should be logged separately rather than lumped into carbs or ignored.

Proposed Syntax

crono quick-add -p 58 -c 96 -f 71 -a 143 --meal Dinner
crono quick-add --protein 58 --carbs 96 --fat 71 --alcohol 143 --meal Dinner

Prerequisites

This feature requires the user to first set up a custom "Alcohol" macro in Cronometer:

• Cronometer supports custom biometrics/macros
• User would need to configure this manually in their Cronometer settings before using the flag
• CLI should document this setup requirement

Acceptance Criteria

• Add -a / --alcohol <grams> flag
• Log to user's custom Alcohol macro in Cronometer
• Document required Cronometer setup in README
• Graceful error if user hasn't configured custom macro