feat: Add OAuth rate limits and usage dashboard #8911

Summary

Add visibility into OAuth rate limits and usage information, particularly useful for Claude Max users who need to monitor their 5-hour and 7-day usage limits.

Problem

Users with Claude Max subscriptions currently have no visibility into their rate limits. This makes it difficult to:

• Know when they're approaching limits
• Understand why requests might be failing
• See which OAuth account is currently active (for multi-account setups)

Proposed Solution

Desktop App

Add a new dialog accessible from the sidebar that displays:

• Provider list with account counts
• Anthropic Usage Limits: 5-hour and 7-day utilization with progress bars
• Account Status: Active/inactive state, cooldown status, request counts
• Color-coded progress bars (green → yellow → red)
• Reset time countdown

CLI

Add a new opencode auth usage command that displays:

• Account status per provider
• Request success/failure counts
• Cooldown state
• Anthropic rate limit percentages

API

Add GET /auth/usage endpoint that returns usage data for all OAuth providers.

Technical Approach

1. Backend

   • Add Auth.OAuthPool.getUsage() - Returns account health and status
   • Add Auth.OAuthPool.fetchAnthropicUsage() - Fetches rate limits from Anthropic's OAuth usage API
   • Add /auth/usage API endpoint

2. Frontend

   • New DialogAuthUsage component with SolidJS
   • Progress bar visualization with color coding
   • Sidebar button integration

3. CLI

   • New AuthUsageCommand subcommand

Additional Context

This feature builds on the OAuth multi-account failover system. It leverages the existing health tracking to provide meaningful usage statistics.

The Anthropic usage API (https://api.anthropic.com/api/oauth/usage) provides utilization percentages and reset times for:

• 5-hour rolling limit
• 7-day limit (all models)
• 7-day limit (Sonnet-specific)