Add /usage endpoint with token tracking, live balances, and cost calculations

CLAUDE.md

@@ -5,8 +5,9 @@ Anthropic-compatible proxy that routes AI requests to multiple providers based o
 
 ## File Structure
 - `proxy.mjs` - Main proxy server (zero dependencies, Node.js built-ins only)
-- `config.json` - API keys and auth token (gitignored)
+- `config.json` - API keys, auth token, and pricing (gitignored)
 - `config.example.json` - Template config
+- `usage-data.json` - Token usage tracking, auto-generated and gitignored
 - `ein-ai-proxy.service` - Systemd unit file
 - `deploy.sh` - Deployment and testing script
 - `sync-context.sh` - Syncs global context to Claude Code and Roo Code
@@ -14,6 +15,7 @@ Anthropic-compatible proxy that routes AI requests to multiple providers based o
 ## Development
 Run locally: `node proxy.mjs` (requires `config.json`)
 Test health endpoint: `curl http://localhost:3100/health`
+Check usage: `curl http://localhost:3100/usage`
 Zero npm dependencies — do not add any.
 
 ## Deployment