Feature: CLI command to check subscription usage

Summary

Add a claude usage CLI command (or enhance /cost) that shows subscription usage stats — the same data visible at https://claude.ai/settings/usage — directly in the terminal.

Motivation

Currently, the only way to check how much of your weekly quota you've used is to open the browser and navigate to the settings page. For users who spend most of their time in the terminal with Claude Code, this is a friction point. Knowing remaining usage helps with planning — e.g., whether to tackle a big task now or wait for the quota reset.

Proposed solution

1. Expose a subscription usage API endpoint (e.g., GET /v1/usage/subscription) that returns current period usage, limits, and reset time
2. Add a CLI command (claude usage or similar) that calls this endpoint and displays a formatted summary, e.g.:

Claude Max — Weekly Usage
Messages:  342 / 500  (68%)
Reset:     2026-03-28 (3 days)

Alternatives considered

• /cost exists but only shows session-level token counts, not subscription quota
• Scraping the web UI is fragile and requires browser session auth
• No documented API currently exists for subscription usage data

Additional context

This would also benefit automation — users could set up alerts when approaching their limit, or integrate usage tracking into their workflows.