Feature: Add date flag to quick-add command

[milldr]

Summary

Add a -d / --date flag to crono quick-add to allow logging entries to past (or future) dates.

Use Case

When logging meals retroactively (e.g., yesterday's dinner), users currently have to:

1. Log via CLI (goes to today)
2. Manually drag the entry to the correct date in the Cronometer app

A date flag would allow direct logging to the intended date.

Proposed Syntax

crono quick-add -p 58 -c 96 -f 71 --meal Dinner -d 2026-02-14
crono quick-add -p 58 -c 96 -f 71 --meal Dinner --date yesterday

Acceptance Criteria

• Accept ISO date format (YYYY-MM-DD)
• Accept relative dates (yesterday, -1d)
• Default to today if flag not provided (current behavior)