fix(gateway-client): increase chat completion timeout from 30s to 120s, add retry on timeout

- Add configurable chatRunTimeoutMs option (default 120s) to GatewayClientOptions
- Bump RPC request timeout from 15s to 30s
- Mark 'Timed out waiting for chat completion' as recoverable for auto-retry
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>