Add usage visibility for Claude Max subscribers

Problem

On Claude Max, there's no way to see how much of your daily usage allowance you've consumed or when it resets. The only signal is getting rate-limited, which is disruptive — especially if it happens right before a deadline.

The /context command shows the conversation's token window, but that's a different concept and doesn't help with usage planning.

Proposal

Add a command (e.g. /usage) that shows:

• Approximate % of daily allowance used
• Time until reset

Even a rough indicator would be a big improvement over the current experience of flying blind.