Support 24-hour time format in /usage display

Feature Request

The /usage command displays reset times in 12-hour AM/PM format (e.g. 2:30 PM). It would be great to support 24-hour format (e.g. 14:30) — either by respecting the system locale or via a user setting.

Motivation

Many users (especially outside the US) prefer or exclusively use 24-hour time. The current 12-hour display is hardcoded and not configurable.

Suggested Approach

• Respect the system locale's time format preference, or
• Add a timeFormat setting (e.g. in .claude/settings.json) with "12h" / "24h" options