Fixes, readme

Drop cli-proxy-api token handling, use only native Claude credentials.
Simplify refresh to single endpoint (platform.claude.com) with scope.
Add debug/refresh and debug/shutdown endpoints. Graceful shutdown.

config.example.yaml

@@ -1,7 +1,6 @@
 port: 8082
 api_keys:
   - "your-proxy-api-key"
-auth_dir: ""
 claude_credentials: "~/.claude/.credentials.json"
 claude_binary: "claude"